SEI INSTITUTIONAL MANAGED TRUST

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SEI INSTITUTIONAL MANAGED TRUST

Large Cap Value Fund Small Cap Fund Small Cap Value Fund Small Cap Growth Fund Tax-Managed Small/Mid Cap Fund

(the “Funds”)

Supplement dated January 15, 2016

to the Class A Shares Prospectus (the “Prospectus”) dated January 31, 2015, as amended on July 17, 2015, November 6, 2015 and December 17, 2015

This Supplement provides new and additional information beyond that contained in the Class A Shares Prospectus and should be read in conjunction with such Prospectus.

The Prospectus is hereby amended and supplemented to reflect the following changes to the Funds. Change in the Large Cap Value Fund’s Portfolio Management

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Large Cap Value Fund, the text relating to AJO, L.P. is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

Experience with

Sub-Adviser Portfolio Manager the Fund Title with Sub-Adviser

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Large Cap Value Fund,” the text relating to AJO, L.P. is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

AQR Capital Management, LLC: AQR Capital Management, LLC (AQR), located at 2 Greenwich Plaza, 4th Floor, Greenwich, Connecticut 06830, serves as a Sub-Adviser to the Large Cap Value Fund. Clifford S. Asness, Ph.D., M.B.A., Jacques A. Friedman, M.S., Ronen Israel, M.A., and Lars N. Nielsen, M.Sc. manage the portion of the Large Cap Value Fund’s assets allocated to AQR. Dr. Asness, Managing and Founding Principal, co-founded AQR in 1998 and has been responsible for the day-to-day management of the firm’s investment strategies since 1998. Mr. Friedman, Principal, Head of Global Stock Selection, joined AQR at its inception in 1998, and oversees research and portfolio management for the firm’s equity products and strategies. Mr. Israel, Principal, joined AQR in 1999 and co-founded the Global Stock Selection team before founding the Global Alternative Premia group, focusing on portfolio management and research. Mr. Nielsen, Principal, joined AQR in 2000, and oversees research in the Global Stock Selection and Global Asset Allocation teams. He is also part of the portfolio management teams for several hedge funds and long-only portfolios. There are no other changes to the portfolio management of the Large Cap Value Fund.

Changes to the Small Cap Fund’s Principal Investment Strategies and Sub-Advisers

In the Small Cap Fund’s “Principal Investment Strategies” section, the text is hereby deleted and replaced with the following:

Under normal circumstances, the Small Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities (both common and preferred stocks) of small companies, including exchange-traded funds (ETFs) based on small capitalization indices and securities of real estate investment trusts (REITs). For purposes of this Fund, a small company is a company with a market capitalization in the range of companies in the Russell 2000 Index (between $20 million and $7.3 billion as of December 31, 2014), as determined at the time of purchase. The market capitalization range and the composition of the Russell 2000 Index are subject to change. The Fund may also invest in warrants and, to a lesser extent, in securities of large capitalization companies.

The Fund uses a multi-manager approach, relying primarily upon a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation, the Fund’s adviser (SIMC or the Adviser). Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. In managing its portion of the Fund’s assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.

Managing and Founding Principal Since 2016

Clifford S. Asness, Ph.D., M.B.A. AQR Capital Management, LLC

Principal, Head of Global Stock Selection Since 2016

Jacques A. Friedman, M.S.

Principal Since 2016

Ronen Israel, M.A

Lars N. Nielsen, M.Sc.

Merrill Corp - SEI Institutional Managed Trust Class A Prospectus Supplement [Funds] 033-09504 01-15-2...ED [AUX] | jcarlso | 15-Jan-16 13:57 | 16-2010-2.ba |

Sequence: 1

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The Fund implements the investment recommendations of SIMC and its Sub-Advisers through the use of an overlay manager appointed by SIMC. Each Sub-Adviser provides a model portfolio to the Fund on an ongoing basis that represents that Sub-Adviser’s recommendation as to the securities to be purchased, sold or retained by the Fund. The overlay manager then constructs a portfolio for the Fund that represents the aggregation of the model portfolios of the Sub-Advisers and SIMC with the weighting of each Sub-Adviser’s model in the total portfolio determined by SIMC.

Pursuant to direction from SIMC, the overlay manager has limited authority to vary from the models. For example, SIMC may direct the overlay manager to adjust the portfolio to implement SIMC’s forward looking views regarding various portfolio characteristics or factors, or for risk management purposes. The overlay manager may also vary the portfolio implementation to seek trading cost efficiencies, loss harvesting, portfolio rebalancing or other portfolio construction objectives as directed by SIMC.

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Small Cap Fund, the text relating to Integrity Asset Management (a franchise within the registered adviser Victory Capital Management Inc.) is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Small Cap Fund,” the text relating to Integrity Asset Management (a franchise within the registered adviser Victory Capital Management Inc.) is hereby deleted and replaced text with the following in the appropriate alphabetical order thereof:

Falcon Point Capital, LLC: Falcon Point Capital, LLC (Falcon Point), located at Two Embarcadero Center, Suite 420, San Francisco, California 94111 serves as a Sub-Adviser to the Small Cap Fund. A team of investment professionals manages the portion of the Small Cap Fund allocated to Falcon Point. Michael L. Thomas, Senior Portfolio Manager, joined Falcon Point in 2002 from Dresdner RCM Global Investors, where he worked as part of a team managing a small cap growth portfolio. Prior to joining Dresdner RCM, Mr. Thomas worked as a sell-side research analyst covering various segments of the computer services industry for both Salomon Smith Barney and Montgomery Securities. Before entering the investment profession, he worked as a consultant for Andersen Consulting (now known as Accenture) focusing on custom computer system design and implementation. Mr. Thomas earned a B.A., Magna Cum Laude, in Finance from Loyola University in Maryland and an MBA with Honors from Columbia Business School. James A. Bitzer, CFA, Senior Managing Director and Director of Research, joined Falcon Point in 1998 from Prudential Investments, where he was Managing Director and Senior Portfolio Manager of the US Small Cap team. Mr. Bitzer spent a year in London managing Prudential’s European small cap operations. Prior to his tenure as Managing Director, Mr. Bitzer served as Vice President, Corporate Finance of the Prudential Capital Group, where he originated and managed a portfolio of over $2 billion of debt, mezzanine and equity securities. Before his money management career, Mr. Bitzer worked as a financial analyst for Raytheon. Mr. Bitzer earned a B.A., Magna Cum Laude, in Business Economics from the University of California, Santa Barbara and an MBA with Honors in Finance from the University of Michigan Business School. Michael J. Mahoney, Senior Managing Director and Portfolio Manager, joined Falcon Point Capital in 2001 from Interwoven, where he was Director of Investor Relations. He held this position since 2000 when Interwoven acquired Neonyoyo, a wireless software startup where he was Chief Strategy Officer. Prior to Interwoven, Mr. Mahoney was an investment manager in San Francisco for 9 years, specializing in telecommunications, technology and media investments. Mr. Mahoney was Director of the Global Telemedia Group at Dresdner RCM Global Investors from 1999 to 2000. Previously he was Portfolio Manager of the GT (later AIM) Global Telecommunications fund and an analyst for GT Capital Management in San Francisco from 1991 to 1999. Before his money management career, Mr. Mahoney worked as a consultant at Bain & Company in Boston and as a corporate finance analyst at E. F. Hutton & Co. in New York. Mr. Mahoney has an MBA from the Stanford Graduate School of Business and a B.A. from Whitman College, where he was elected to Phi Beta Kappa and now serves on the Board of Overseers (emeritus) and the Investment Committee.

Parametric Portfolio Associates LLC: Parametric Portfolio Associates LLC (Parametric), located at 1918 Eighth Avenue, Suite 3100, Seattle, Washington 98101, serves as a Sub-Adviser to the Small Cap Fund. A team of investment professionals at Parametric, led by Paul Bouchey, Chief Investment Officer—Seattle Investment Center, and Thomas Seto, Head of Investment Management—Seattle Investment Center, manages the portion of the Small Cap Fund’s assets allocated to Parametric. Messrs. Bouchey and Seto have been with Parametric since 2006 and 1998, respectively. There are no other changes to the principal investment strategies or portfolio management of the Small Cap Fund.

Changes to the Small Cap Value Fund’s Principal Investment Strategies and Sub-Advisers

In the Small Cap Value Fund’s “Principal Investment Strategies” section, the text is hereby deleted and replaced with the following:

Under normal circumstances, the Small Cap Value Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small companies. The Fund will primarily seek to purchase securities believed to be attractively valued in relation to various measures which may include earnings, capital structure or return on invested capital. For the purpose of this Fund, a small company is a company with a market capitalization in the range of companies in the Russell 2000 Index (between $20 million and $7.3 billion as of December 31, 2014), as determined at the time of purchase. The market capitalization range and the composition of the Russell 2000 Index are subject to change.

Falcon Point Capital, LLC Michael L. Thomas Since 2016 Senior Portfolio Manager

James A. Bitzer Since 2016 Senior Managing Director

Michael J. Mahoney Since 2016 Senior Managing Director

Parametric Portfolio Associates LLC

Paul Bouchey Since 2016 Chief Investment Officer—Seattle

Investment Center

Thomas Seto Since 2016 Head of Investment Management—

Seattle Investment Center Sequence: 2

CHKSUM Content: 14016 Layout: 48739 Graphics: No Graphics CLEAN

JOB: 16-2010-2 CYCLE#;BL#: 1; 0 TRIM: 8.5" x 11" AS: Merrill Woburn: 781-939-0500 COMPOSITE

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The Fund’s investments in equity securities may include common and preferred stocks, warrants, and, to a lesser extent, real estate investment trusts (REITs), exchange-traded funds (ETFs) and securities of large capitalization companies.

The Fund uses a multi-manager approach, relying primarily upon a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation, the Fund’s adviser (SIMC or the Adviser). Assets of the Fund not allocated to a Sub-Adviser are managed directly by SIMC. In managing its portion of the Fund’s assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Small Cap Value Fund, the text relating to LMCG Investments, LLC, Martingale Asset Management L.P., Security Capital Research & Management Incorporated and William Blair Investment

Management, LLC is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof: Experience

with

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Small Cap Value Fund,” the text relating to LMCG Investments, LLC, Martingale Asset Management L.P., Security Capital Research & Management Incorporated and William Blair Investment Management, LLC is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

AQR Capital Management, LLC: AQR Capital Management, LLC (AQR), located at 2 Greenwich Plaza, 4th Floor, Greenwich, Connecticut 06830, serves as a Sub-Adviser to the Small Cap Value Fund. Clifford S. Asness, Ph.D., M.B.A., Jacques A. Friedman, M.S., Ronen Israel, M.A., and Lars N. Nielsen, M.Sc. manage the portion of the Small Cap Value Fund’s assets allocated to AQR. Dr. Asness, Managing and Founding Principal, co-founded AQR in 1998 and has been responsible for the day-to-day management of the firm’s investment strategies since 1998. Mr. Friedman, Principal, Head of Global Stock Selection, joined AQR at its inception in 1998, and oversees research and portfolio management for the firm’s equity products and strategies. Mr. Israel, Principal, joined AQR in 1999 and co-founded the Global Stock Selection team before founding the Global Alternative Premia group, focusing on portfolio management and research. Mr. Nielsen, Principal, joined AQR in 2000, and oversees research in the Global Stock Selection and Global Asset Allocation teams. He is also part of the portfolio management teams for several hedge funds and long-only portfolios. Cardinal Capital Management, L.L.C.: Cardinal Capital Management, L.L.C. (Cardinal), located at Four Greenwich Office Park, Greenwich, Connecticut 06831 serves as a Sub-Adviser to the Small Cap Value Fund. A team of investment professionals manages the portion of the Small Cap Value Fund allocated to Cardinal. Eugene Fox, Robert Kirkpatrick and Rachel Matthews have all been with Cardinal for more than 14 years. Mr. Fox is a Managing Partner and Portfolio Manager of the Sub-Adviser. Before joining the Sub-Adviser in 1995, Mr. Fox was a managing director with Deltec Asset Management where he and a retired Managing Partner of the Sub-Adviser built the value equity investment management business. Mr. Fox

AQR Capital Management, LLC Clifford S. Asness, Ph.D., M.B.A. Since 2016 Managing and Founding Principal

Jacques A. Friedman, M.S. Since 2016 Principal, Head of Global Stock Selection

Ronen Israel, M.A Since 2016 Principal

Lars N. Nielsen, M.Sc. Since 2016 Principal

Anne Wickland, CFA Since 2016 Portfolio Manager, Principal

Cardinal Capital Management, L.L.C.

Eugene Fox III Since 2016 Portfolio Manager

Robert B. Kirkpatrick, CFA Since 2016 Portfolio Manager

Rachel D. Matthews Since 2016 Portfolio Manager

Robert Fields Since 2016 Portfolio Manager

Snow Capital Management, L.P. Joshua Schachter, CFA Since 2016 Senior Portfolio Manager, Principal

Paul Bouchey Since 2016 Chief Investment Officer—Seattle

Investment Center

Thomas Seto Since 2016 Head of Investment Management—

Seattle Investment Center

Sequence: 3

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joined Deltec in 1993 from D.S. Kennedy & Co., a small cap value equity firm, where he was an investment analyst. Prior to joining D.S. Kennedy & Co., he held financial positions at FMC Corporation from 1984 to 1991. These included positions as the director of pension investments and manager of corporate finance. Mr. Fox received his B.A. in economics from the University of Virginia and his MBA from the University of Chicago Graduate School of Business. Mr. Kirkpatrick is a Managing Partner and Portfolio Manager of the Sub-Adviser. Prior to joining the Sub-Adviser in 2000, Mr. Kirkpatrick was a partner at Breeco Management, a research driven equity hedge fund. Previously, Mr. Kirkpatrick held senior equity portfolio management positions with Unifund S.A., a Swiss-based global private investment company. Mr. Kirkpatrick also served for six years as a managing director at Bigler/Crossroads, a venture capital and small cap investment management firm. Mr. Kirkpatrick began his investment career in 1985 at CIGNA Corporation where he was a sector portfolio manager. While at CIGNA, Mr. Kirkpatrick also analyzed the electric utility, telecommunications, aerospace, and airline industries. Mr. Kirkpatrick received his B.A. in economics from the Williams College and earned the CFA professional

designation in 1988. Ms. Matthews is a Partner and Portfolio Manager of the Sub-Adviser. Prior to joining the Sub-Adviser in 2001, Ms. Matthews was a high yield bond trader at Oppenheimer Funds, Inc. from 1996 to 1999. Ms. Matthews traded U.S. government securities at HSBC Securities from 1994 to 1996. Previously, Ms. Matthews was a private placement credit analyst at the Mutual Life Insurance Company of New York. Ms. Matthews received her B.A. in economics from Columbia University and her MBA from New York University. Mr. Fields has been in the investment industry since 1998. Prior to joining Cardinal in 2013, Mr. Fields was a partner and portfolio manager for two years at Ana Capital Management, a long-biased opportunistic value investment firm. Previously, Mr. Fields was a partner and director of research at Breeden Capital Management, a concentrated, long-only investment firm and an analyst covering value equities and distressed debt at MFP Investors, the personal investment firm of Michael F. Price. Parametric Portfolio Associates LLC: Parametric Portfolio Associates LLC (Parametric), located at 1918 Eighth Avenue, Suite 3100, Seattle, Washington 98101, serves as a Sub-Adviser to the Small Cap Value Fund. A team of investment professionals at Parametric, led by Paul Bouchey, Chief Investment Officer—Seattle Investment Center, and Thomas Seto, Head of Investment Management—Seattle Investment Center, manages the portion of the Small Cap Value Fund’s assets allocated to Parametric. Messrs. Bouchey and Seto have been with Parametric since 2006 and 1998, respectively.

Snow Capital Management, L.P.: Snow Capital Management, L.P. (SCM), located at 2000 Georgetowne Drive, Suite 200, Sewickley, Pennsylvania 15143, serves as a Sub-Adviser to the Small Cap Value Fund. A team of investment professionals manages the portion of the Small Cap Value Fund’s assets allocated to SCM. Joshua Schachter, CFA is a Senior Portfolio Manager and Principal at SCM, and has been with the firm since its inception in 2001. His responsibilities include research, selection and portfolio management. Anne Wickland, CFA is a Portfolio Manager and Principal at SCM. She joined the firm in 2006 as a Senior Analyst, and was appointed to her current role in 2010.

There are no other changes to the principal investment strategies or portfolio management of the Small Cap Value Fund. Changes to the Small Cap Growth Fund’s Principal Investment Strategies and Sub-Advisers

In the Small Cap Growth Fund’s “Principal Investment Strategies” section, the text is hereby deleted and replaced with the following:

Under normal circumstances, the Small Cap Growth Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small companies. The Fund will primarily seek to purchase securities believed to have attractive growth and appreciation potential. For the purposes of this Fund, a small company is a company with a market capitalization in the range of companies in the Russell 2000 Index (between $20 million and $7.3 billion as of December 31, 2014), as determined at the time of purchase. The market capitalization range and the composition of the Russell 2000 Index are subject to change. The Fund’s investments in equity securities may include common and preferred stocks, warrants and, to a lesser extent, real estate investment trusts (REITs), exchange-traded funds (ETFs) and securities of large capitalization companies.

The Fund uses a multi-manager approach, relying primarily upon a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation, the Fund’s adviser (SIMC or the Adviser). Assets of the Fund not allocated to a Sub-Adviser are managed directly by SIMC. In managing its portion of the Fund’s assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.

Sequence: 4

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In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Small Cap Growth Fund, the text relating to AQR Capital Management, LLC and J.P. Morgan Investment Management Inc. is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Small Cap Growth Fund,” the text relating to AQR Capital Management, LLC and J.P. Morgan Investment Management Inc. is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

Axiom International Investors LLC: Axiom International Investors LLC (Axiom), located at 33 Benedict Place, 2nd Floor, Greenwich, Connecticut 06830 serves as a Sub-Adviser to the Small Cap Growth Fund. A team of investment professionals manages the portion of the Small Cap Growth Fund allocated to Axiom. Matthew A. Franco, CFA, is the Lead Portfolio Manager for the Axiom Global and International Micro-Cap Equity Funds and Co-Portfolio Manager for the US Small Cap Equity Strategy and the International Small-Cap Equity Strategy. Mr. Franco was one of the original investment team members at Axiom’s inception in 1998. Prior to Axiom, Mr. Franco was an Associate at Columbus Circle Investors, a unit of PIMCO Advisors LP, where he was an Analyst for the International Fund. Mr. Franco was also affiliated with investment boutique R.L. Renck & Company, a small

capitalization company specialist firm. Mr. Franco has the designation of Chartered Financial Analyst and is a member of the New York Society of Security Analysts. Mr. Franco holds a B.S. summa cum laude in Finance with a concentration in Asian Studies from Saint John’s University. David Kim, CFA, is the Lead Portfolio Manager for the Axiom US Small Cap Equity Strategy and Co-Portfolio Manager for the Axiom Global and International Micro-Cap Funds. Prior to joining Axiom, Mr. Kim was a Research Analyst for small and micro-capitalization companies at Pinnacle Associates LTD. Mr. Kim is a Chartered Financial Analyst and a member of the New York Society of Security Analysts. Mr. Kim holds a B.S. degree in Business

Administration from Georgetown University, with a double major in Finance and International Business. Mr. Kim also attended Georgetown University’s Corporate Business Program at the Chinese University of Hong Kong.

Falcon Point Capital, LLC: Falcon Point Capital, LLC (Falcon Point), located at Two Embarcadero Center, Suite 420, San Francisco, California 94111 serves as a Sub-Adviser to the Small Cap Growth Fund. A team of investment professionals manages the portion of the Small Cap Growth Fund allocated to Falcon Point. Michael L. Thomas, Senior Portfolio Manager, joined Falcon Point in 2002 from Dresdner RCM Global Investors, where he worked as part of a team managing a small cap growth portfolio. Prior to joining Dresdner RCM, Mr. Thomas worked as a sell-side research analyst covering various segments of the computer services industry for both Salomon Smith Barney and Montgomery Securities. Before entering the investment profession, he worked as a consultant for Andersen Consulting (now known as Accenture) focusing on custom computer system design and implementation. Mr. Thomas earned a B.A., Magna Cum Laude, in Finance from Loyola University in Maryland and an MBA with Honors from Columbia Business School. James A. Bitzer, CFA, Senior Managing Director and Director of Research, joined Falcon Point in 1998 from Prudential Investments, where he was Managing Director and Senior Portfolio Manager of the US Small Cap team. Mr. Bitzer spent a year in London managing Prudential’s European small cap operations. Prior to his tenure as Managing Director, Mr. Bitzer served as Vice President, Corporate Finance of the Prudential Capital Group, where he originated and managed a portfolio of over $2 billion of debt, mezzanine and equity securities. Before his money management career, Mr. Bitzer worked as a financial analyst for Raytheon. Mr. Bitzer earned a B.A., Magna Cum Laude, in Business Economics from the University of California, Santa Barbara and an MBA with Honors in Finance from the University of Michigan Business School. Michael J. Mahoney, Senior Managing Director and Portfolio Manager, joined Falcon Point Capital in 2001 from Interwoven, where he was Director of Investor Relations. He held this position since 2000 when Interwoven acquired Neonyoyo, a wireless software startup where he was Chief Strategy Officer. Prior to

Interwoven, Mr. Mahoney was an investment manager in San Francisco for 9 years, specializing in telecommunications, technology and media investments. Mr. Mahoney was Director of the Global Telemedia Group at Dresdner RCM Global Investors from 1999 to 2000. Previously he was Portfolio Manager of the GT (later AIM) Global Telecommunications fund and an analyst for GT Capital Management in San Francisco from 1991 to 1999. Before his money management career, Mr. Mahoney worked as a consultant at Bain & Company in Boston and as a corporate finance analyst at E. F. Hutton & Co. in New York. Mr. Mahoney has an MBA from the Stanford Graduate School of Business and a B.A. from Whitman College, where he was elected to Phi Beta Kappa and now serves on the Board of Overseers (emeritus) and the Investment Committee.

Parametric Portfolio Associates LLC: Parametric Portfolio Associates LLC (Parametric), located at 1918 Eighth Avenue, Suite 3100, Seattle, Washington 98101, serves as a Sub-Adviser to the Small Cap Growth Fund. A team of investment professionals at Parametric, led by Paul Bouchey, Chief Investment Officer—Seattle Investment Center, and Thomas Seto, Head of Investment Management—Seattle Investment Center, manages the portion of the Small Cap Growth Fund’s assets allocated to Parametric. Messrs. Bouchey and Seto have been with Parametric since 2006 and 1998, respectively.

There are no other changes to the principal investment strategies or portfolio management of the Small Cap Growth Fund.

Head of Investment Management— Seattle Investment Center

Since 2016 Thomas Seto

Chief Investment Officer—Seattle Investment Center

Since 2016 Paul Bouchey

Senior Managing Director Since 2016

Michael J. Mahoney

Portfolio Manager Since 2006

David Kim, CFA Axiom International Investors LLC

Matthew Franco, CFA

Senior Portfolio Manager Since 2016

Michael L. Thomas Falcon Point Capital, LLC

Senior Managing Director Since 2016

James A. Bitzer

Sequence: 5

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Changes to the Tax-Managed Small/Mid Cap Fund’s Sub-Advisers

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Tax-Managed Small/Mid Cap Fund, the text relating to LMCG Investments, LLC and William Blair Investment Management, LLC is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Tax-Managed Small/Mid Cap Fund,” the text relating to LMCG Investments, LLC and William Blair Investment Management, LLC is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

AQR Capital Management, LLC: AQR Capital Management, LLC (AQR), located at 2 Greenwich Plaza, 4th Floor, Greenwich, Connecticut 06830, serves as a Sub-Adviser to the Tax-Managed Small/Mid Cap Fund. Clifford S. Asness, Ph.D., M.B.A., Jacques A. Friedman, M.S., Ronen Israel, M.A., and Lars N. Nielsen, M.Sc. manage the portion of the Tax-Managed Small/Mid Cap Fund’s assets allocated to AQR. Dr. Asness, Managing and Founding Principal, co-founded AQR in 1998 and has been responsible for the day-to-day management of the firm’s investment strategies since 1998.

Mr. Friedman, Principal, Head of Global Stock Selection, joined AQR at its inception in 1998, and oversees research and portfolio management for the firm’s equity products and strategies. Mr. Israel, Principal, joined AQR in 1999 and co-founded the Global Stock Selection team before founding the Global Alternative Premia group, focusing on portfolio management and research. Mr. Nielsen, Principal, joined AQR in 2000, and oversees research in the Global Stock Selection and Global Asset Allocation teams. He is also part of the portfolio management teams for several hedge funds and long-only portfolios.

Cardinal Capital Management, L.L.C.: Cardinal Capital Management, L.L.C. (Cardinal), located at Four Greenwich Office Park, Greenwich,

Connecticut 06831 serves as a Sub-Adviser to the Tax-Managed Small/Mid Cap Fund. A team of investment professionals manages the portion of the Tax-Managed Small/Mid Cap Fund allocated to Cardinal. Eugene Fox, Robert Kirkpatrick and Rachel Matthews have all been with Cardinal for more than 14 years. Mr. Fox is a Managing Partner and Portfolio Manager of the Sub-Adviser. Before joining the Sub-Adviser in 1995, Mr. Fox was a managing director with Deltec Asset Management where he and a retired Managing Partner of the Sub-Adviser built the value equity investment management business. Mr. Fox joined Deltec in 1993 from D.S. Kennedy & Co., a small cap value equity firm, where he was an investment analyst. Prior to joining D.S. Kennedy & Co., he held financial positions at FMC Corporation from 1984 to 1991. These included positions as the director of pension investments and manager of corporate finance. Mr. Fox received his B.A. in economics from the University of Virginia and his MBA from the University of Chicago Graduate School of Business. Mr. Kirkpatrick is a Managing Partner and Portfolio Manager of the Sub-Adviser. Prior to joining the Sub-Adviser in 2000, Mr. Kirkpatrick was a partner at Breeco Management, a research driven equity hedge fund. Previously, Mr. Kirkpatrick held senior equity portfolio management positions with Unifund S.A., a Swiss-based global private investment company. Mr. Kirkpatrick also served for six years as a managing director at Bigler/Crossroads, a venture capital and small cap investment management firm. Mr. Kirkpatrick began his investment career in 1985 at CIGNA Corporation where he was a sector portfolio manager. While at CIGNA, Mr. Kirkpatrick also analyzed the electric utility, telecommunications, aerospace, and airline industries. Mr. Kirkpatrick received his B.A. in economics from the Williams College and earned the CFA professional designation in 1988. Rachel Matthews is a Partner and Portfolio Manager of the Sub-Adviser. Prior to joining the Sub-Adviser in 2001, Ms. Matthews was a high yield bond trader at Oppenheimer Funds, Inc. from 1996 to 1999. Ms. Matthews traded U.S. government securities at HSBC Securities from 1994 to 1996. Previously, Ms. Matthews was a private placement credit analyst at the Mutual Life Insurance Company of New York. Ms. Matthews received her B.A. in economics from Columbia University and her MBA from New York University. Robert Fields has been in the investment industry since 1998. Prior to joining Cardinal in 2013, Mr. Fields was a partner and portfolio manager for two years at Ana Capital Management, a long-biased opportunistic value investment firm. Previously, Mr. Fields was a partner and director of research at Breeden Capital Management, a concentrated, long-only investment firm and an analyst covering value equities and distressed debt at MFP Investors, the personal investment firm of Michael F. Price.

Fiduciary Management Associates, LLC: Fiduciary Management Associates, LLC (FMA), located at 55 West Monroe Street, Suite 2550, Chicago, Illinois 60603, serves as a Sub-Adviser to the Tax-Managed Small/Mid Cap Fund. Kathryn A. Vorisek, Senior Managing Director, Chief Investment Officer and Small/SMID Cap Portfolio Manager, and Leo Harmon, CFA, Managing Director, Director of Research and Small/SMID Cap Portfolio Manager, manage the portion of the Tax-Managed Small/Mid Cap Fund’s assets allocated to FMA. As Chief Investment Officer, Ms. Vorisek is

Leo Harmon, CFA Since 2016 Managing Director, Director of Research

and Small/SMID Cap Portfolio Manager Senior Managing Director, Chief Investment Officer and Small/SMID Cap Portfolio Manager Since 2016 Kathryn A. Vorisek Fiduciary Management Associates, LLC Portfolio Manager Since 2016 Rachel D. Matthews Portfolio Manager Since 2016 Robert Fields Portfolio Manager Since 2016

Eugene Fox III Cardinal Capital

Management, L.L.C.

Robert B. Kirkpatrick, CFA

Managing and Founding Principal Since 2016

Clifford S. Asness, Ph.D., M.B.A. AQR Capital Management, LLC

Principal, Head of Global Stock Selection Since 2016

Jacques A. Friedman, M.S.

Ronen Israel, M.A

Lars N. Nielsen, M.Sc. Sequence: 6

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responsible for determining the overall strategic direction of the portfolio and retains the ultimate authority for specific investment decisions. She is supported in the role by Mr. Harmon, who also serves as portfolio manager, and by a team of analysts who share responsibility for sector and company specific analysis. Ms. Vorisek joined FMA in 1996 and was appointed FMA’s Chief Investment Officer in 2000. She also has analytical responsibility for the consumer staples and energy sectors. Ms. Vorisek possesses more than 32 years of experience in the investment industry and holds a B.S. in Finance from Marquette University and an M.B.A. from the Kellogg Graduate School of Management at Northwestern University in Finance and International Business. Mr. Harmon joined FMA in 2003 and manages the firm’s research efforts; he also has analytical responsibility for the financial services-banking sector. Mr. Harmon has more than 22 years of industry experience as a portfolio manager and research analyst covering a variety of industries in both larger and smaller market capitalizations, with expertise in financial services. Prior to joining FMA, Mr. Harmon was a portfolio manager at Allstate Insurance, Allstate Investments LLC. He earned a B.S. from Bradley University and an M.B.A. from Duke University.

There are no other changes to the principal investment strategies or portfolio management of the Tax-Managed Small/Mid Cap Fund.

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE SEI-F-988 (01/16)

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SEI INSTITUTIONAL MANAGED TRUST

Multi-Strategy Alternative Fund (the “Fund”)

Supplement dated December 17, 2015

to the Class A Shares Prospectus (the “Prospectus”) dated January 31, 2015, as amended on July 17, 2015 and November 6, 2015

The Prospectus is hereby amended and supplemented to reflect the following changes to the fees and expenses and portfolio management of the Fund.

Restatement of the Fees and Expenses for the Fund

Under the section titled “Fund Summary,” under the heading entitled “Fees and Expenses,” under the sub-heading entitled “Annual Fund Operating Expenses,” the table is hereby deleted and replaced with the following in order to reflect the Fund’s current fees and expenses:

(expenses that you pay each year as a

percentage of the value of your investment)^ Class A Shares Management Fees 1.50% Distribution (12b-1) Fees None Other Expenses

Dividends on Shorts 0.02% Remainder of Other Expenses 0.58%

Total Other Expenses 0.60% Acquired Funds Fees and Expenses (AFFE)† 0.91% Total Annual Fund Operating Expenses 3.01%

^ Total Annual Fund Operating Expenses have been restated to reflect current fees.

† AFFE is based on estimated amounts for the current fiscal year. The Fund incurred AFFE during the most recent fiscal year, and therefore the

operating expenses in this fee table will not correlate to the expense ratio in the Fund’s financial statements (or the “Financial Highlights” section in the prospectus) because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.

In addition, under the same heading, under the sub-heading entitled “Example,” the table is hereby deleted and replaced with the following:

1 Year 3 Years 5 Years 10 Years Multi-Strategy Alternative Fund—Class A Shares $304 $930 $1,582 $3,327

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Information About Fee Waivers,” the text referring to the Multi-Strategy Alternative Fund in the second table is hereby deleted and replaced with the following:

Expected Total Annual Expected Total Annual Fund Fund Operating Operating Expenses (after Expected Total Annual Expected Total Annual Expenses fee waivers, excluding AFFE, Fund Operating Fund Operating (after fee waivers, interest expense and after Expenses Expenses excluding AFFE, commission recapture, Fund Name—Class A Shares (before fee waivers) (after fee waivers) if applicable)* if applicable)* Multi-Strategy Alternative Fund 3.01% 1.42% 0.51% 0.51% There are no further changes to the fees and expenses of the Fund.

Change in the Portfolio Management of the Fund

Under the section titled “Fund Summary,” under the heading entitled “Principal Investment Strategies,” the third paragraph is hereby deleted in its entirety and replaced with the following:

The Fund currently allocates assets to Sub-Advisers pursuant to SIMC’s “manager of managers” model, and the Sub-Advisers manage a portion of the Fund’s portfolio under the general supervision of SIMC. In addition, SIMC may directly manage a portion of the Fund’s assets, which may include allocating assets to investments in Underlying Funds selected by SIMC.

Sequence: 1

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In addition, under the section titled “Fund Summary,” under the heading entitled “Management,” in the table under the sub-heading entitled “Sub-Adviser and Portfolio Managers,” the following text is added in the appropriate alphabetical order thereof:

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” under the heading entitled “Multi-Strategy Alternative Fund,” the following text is hereby added in the appropriate alphabetical order thereof:

Mountaineer Partners Management, LLC: Mountaineer Partners Management, LLC (Mountaineer), located at 150 East 58th Street, 14th Floor, New York, New York 10155 serves as a Sub-Adviser to the Multi-Strategy Alternative Fund. A team of investment professionals headed by Mark Lee manages the portion of the Multi-Strategy Alternative Fund allocated to Mountaineer. Mr. Lee is the Founder and Managing Member of Mountaineer, an opportunistic value and event hedge fund founded in 2011 that invests long and short in equity and debt. Prior to founding Mountaineer, Mr. Lee worked at Contrarian Capital Management, LLC (“Contrarian”) from 1999 to 2011. He joined Contrarian as a distressed debt analyst, and then in 2003 founded and was the sole Portfolio Manager for the Contrarian Long Short Fund for eight years until he departed to launch Mountaineer in

January 2011. In late 2008, Mr. Lee also assumed management of the Contrarian Distressed Equity Fund, which he managed until his departure in January 2011. Both Contrarian Long Short and Contrarian Distressed Equity utilized a similar analytical framework to Mountaineer. Prior to Contrarian, Mr. Lee worked as an Associate at Blavin & Co., a concentrated, long-biased value fund, and as an Associate at Centre Partners, a Lazard-affiliated private equity firm. Mr. Lee began his career in finance in 1992 as an investment banker at Credit Suisse First Boston. Mr. Lee received an MBA from Harvard Business School and an AB, Magna Cum Laude, from Harvard College.

Ramius Advisors, LLC: Ramius Advisors, LLC (Ramius) located at 599 Lexington Avenue, 19th Floor, New York, New York 10022 serves as a Sub-Adviser to the Multi-Strategy Alternative Fund. A team of investment professionals manages the portion of the Multi-Strategy Alternative Fund allocated to Ramius. Ethan Johnson is the Portfolio Manager of the Fund. Mr. Johnson is responsible for risk arbitrage investments at the firm. Mr. Johnson joined Ramius in 2007 as a Research Analyst on the Ramius risk arbitrage desk. Andrew Cohen is the Fund Risk Manager for the Fund. Mr. Cohen monitors with respect to the risk arbitrage investments at the firm. Mr. Cohen joined Ramius in 2001.

Other than as set forth herein, there are no other changes to the portfolio management of the Fund.

PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE SEI-F-980 (12/15)

Mountaineer Partners Management, LLC

Mark Lee Since 2015 Managing Member

Ramius Advisors, LLC Ethan Johnson Since 2015 Portfolio Manager

Andrew Cohen Since 2015 Fund Risk Manager

Merrill Corp - SEI Institutional Managed Trust Multi-Strategy Alternative Class A Prospectus Supplement...ED [AUX] | thunt | 17-Dec-15 10:21 | 15-24964-2.ba |

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(10)

SEI INSTITUTIONAL MANAGED TRUST

Small Cap Value Fund Tax-Managed Small/Mid Cap Fund

Multi-Strategy Alternative Fund (the “Funds”)

Supplement dated November 6, 2015

to the Class A Shares Prospectus (the “Prospectus”) dated January 31, 2015, as amended on July 17, 2015

The Prospectus is hereby amended and supplemented to reflect the following changes to the fees and expenses and portfolio management of the Funds.

Restatement of the Fees and Expenses for the Multi-Strategy Alternative Fund

Under the section titled “Fund Summary,” under the heading entitled “Fees and Expenses,” under the sub-heading entitled “Annual Fund Operating Expenses,” the table is hereby deleted and replaced with the following in order to reflect the Fund’s current fees and expenses:

(expenses that you pay each year as a percentage of the value of

your investment)^ Class A Shares

Management Fees 1.50%

Distribution (12b-1) Fees None Other Expenses Dividends on Shorts 0.02% Remainder of Other Expenses 0.61% Total Other Expenses 0.63%

Acquired Funds Fees and Expenses (AFFE)† 1.37%

Total Annual Fund Operating Expenses 3.50%

^ Total Annual Fund Operating Expenses have been restated to reflect current fees.

† AFFE is based on estimated amounts for the current fiscal year. The Fund incurred AFFE during the most recent fiscal year, and therefore the

operating expenses in this fee table will not correlate to the expense ratio in the Fund’s financial statements (or the “Financial Highlights” section in the prospectus) because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.

In addition, under the same heading, under the sub-heading entitled “Example,” the table is hereby deleted and replaced with the following: 1 Year 3 Years 5 Years 10 Years

Multi-Strategy Alternative Fund—Class A Shares $353 $1,074 $1,817 $3,774

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Information About Fee Waivers,” the text referring to the Multi-Strategy Alternative Fund in the second chart is hereby deleted and replaced with the following:

Expected Total Annual Fund Expected Total Operating Expenses Annual Fund (after fee waivers, Expected Total Expected Total Operating Expenses excluding AFFE,

Fund Name—Class A Shares Annual Fund Annual Fund (after fee waivers, interest expense and after Operating Expenses Operating Expenses excluding AFFE, commission recapture, (before fee waivers) (after fee waivers) if applicable)* if applicable)* Multi-Strategy Alternative Fund 3.50% 1.98% 0.61% 0.61% There are no further changes to the fees and expenses of the Fund.

Change in the Multi-Strategy Alternative Fund’s Portfolio Management

Under the section titled “Fund Summary,” under the heading entitled “Principal Investment Strategies,” the third paragraph is hereby deleted in its entirety and replaced with the following:

The Fund currently allocates assets to one Sub-Adviser pursuant to SIMC’s “manager of managers” model, and the Sub-Adviser manages a portion of the Fund’s portfolio under the general supervision of SIMC. In addition, SIMC may directly manage a portion of the Fund’s assets, which may include allocating assets to investments in Underlying Funds selected by SIMC.

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In addition, under the section titled “Fund Summary,” under the heading entitled “Management,” the chart under the sub-heading entitled “Investment Adviser and Portfolio Manager” is hereby deleted and replaced with the following:

Experience with

Portfolio Manager the Fund Title with Adviser

Sub-Adviser and Portfolio Managers.

Experience with

In addition, under the section titled “More Information About Investments,” all text relating to the “Multi-Strategy Alternative Fund” is hereby deleted. In addition, under the section titled “Investment Adviser,” the paragraph before the heading entitled “High Yield Bond Fund” is hereby deleted in its entirety and replaced with the following:

Srdjan Teslic serves as portfolio manager for the Multi-Strategy Alternative Fund. Mr. Teslic currently serves as Senior Investment Analyst of the Alternative Investments Team and joined SIMC in 2009.

Although the Real Return Fund is able to use a multi-manager approach whereby the Fund’s assets would be allocated among multiple Sub-Advisers, the Fund’s assets currently are managed directly by SIMC. SIMC may, in the future, determine to act as a manager of managers with respect to some or all of the Fund’s assets and allocate Fund assets to one or more Sub-Advisers, upon approval from the Board of Trustees. In addition, SIMC may also directly manage a portion of the High Yield Bond and the Multi-Strategy Alternative Funds’ assets in a manner that it believes will help each Fund achieve its investment goals.

In addition, under the section titled “Sub-Advisers,” under the sub-section entitled “Sub-Advisers and Portfolio Managers,” the following text is hereby added directly before the heading entitled “Long/Short Alternative Fund”:

MULTI-STRATEGY ALTERNATIVE FUND:

Emso Partners Limited: Emso Partners Limited (Emso), located at Iron Trades House, 21-24 Grosvenor Place, London, SW1X 7HN, serves as a Sub-Adviser to a portion of the assets of the Multi-Strategy Alternative Fund. A team of investment professionals manages the portion of the Multi-Strategy Alternative Fund’s assets allocated to Emso. Mark Franklin is the Chief Investment Officer of Emso. Mark began his career in international banking in 1979 and lived and worked throughout Latin America holding various positions in Argentina, Colombia and Mexico. He joined Salomon Brothers in 1986 to establish and co-run their emerging markets customer business. Following his appointment to the position of partner in 1991, he joined Salomon’s proprietary trading division where he started and successfully ran the emerging markets investment business until the merger with Citigroup. After the merger he founded the Emso Fund, established Emso Partners Limited (then as a subsidiary of Citibank), and ultimately executed its employee buyout in 2013. During the past 15 years he has built a wide institutional investor base and a consistently strong performance track record in Emso and its associated funds. Mark holds a BA from Brown University in Economics. He is a Trustee of Tusk, a pan-African charitable trust. John Hynes is a portfolio manager focusing on liquid alternative strategies. Before joining Emso in 2011, Mr. Hynes spent 17 years at Fidelity

Investments and Fidelity International, most recently within the Emerging Markets Equity Group, working as a PM for the Fidelity Series Emerging Markets Fund. At Fidelity he also held at various times the positions of Global EM Analyst; European HY Credit Analyst, European Equity Analyst; Co-head of International Fixed Income, and Senior Global Bond Trader. Previously, he worked as a Global Bond Trader at Watermark Management, and began his career as a Research Associate at Temple, Barker & Sloane. John earned an MBA in Finance from The Wharton School, University of Pennsylvania, and a BA in Economics from Dartmouth College.

Other than as set forth herein, there are no other changes to the portfolio management of the Fund. Change in Sub-Adviser for the Small Cap Value and Tax-Managed Small/Mid Cap Funds

Effective October 1, 2015, William Blair & Company L.L.C., which serves as a sub-adviser to the Small Cap Value and Tax-Managed Small/Mid Cap Funds, underwent an internal reorganization, as a result of which the Funds will now be managed by William Blair Investment Management, LLC, pursuant to a new sub-advisory agreement. Therefore, all references to “William Blair & Company L.L.C” are hereby deleted and replaced with “William Blair Investment Management, LLC.”

Other than as set forth herein, there are no other changes to the portfolio management of the Funds. PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE

SEI-F-975 (11/15)

Srdjan Teslic Since 2013 Senior Investment Analyst—Alternative

Investments Team

Emso Partners Limited Mark R. Franklin Since 2015 Founder, Chief Investment Officer

John Hynes Since 2015 Portfolio Manager

Merrill Corp - SEI Institutional Managed Trust Class A Prospectus Supplement [Funds] 033-09504 11-02-2...ED [AUX] | thunt | 06-Nov-15 10:46 | 15-22239-2.ba

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(each, a “Fund” and together, the “Funds”)

Supplement Dated July 17, 2015

to the Class A Shares Prospectus (the “Prospectus”) dated January 31, 2015

The Prospectus is hereby amended and supplemented to reflect the following changes to the Funds. Changes to the Large Cap Fund’s Principal Investment Strategies and Sub-Advisers

In the Large Cap Fund’s “Principal Investment Strategies” section, the text is hereby deleted and replaced with the following:

Under normal circumstances, the Large Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large companies. For purposes of this Fund, a large company is a company with a market capitalization in the range of companies in the Russell 1000 Index (between $275 million and $648 billion as of December 31, 2014) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. These securities may include common stocks, preferred stocks, warrants, American depositary receipts (ADRs) and exchange-traded funds (ETFs). The Fund may also, to a lesser extent, invest in common and preferred stocks of small capitalization companies. The Fund may invest up to 20% of its assets in foreign securities.

The Fund uses a multi-manager approach, relying primarily on a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies and strategies to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation, the Fund’s adviser (SIMC or the Adviser). Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. In managing its portion of the Fund’s assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Large Cap Fund, the text relating to AJO, LP, Brown Advisory, LLC and Waddell & Reed Investment Management Co is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

Sub-Adviser Portfolio Manager Fund Title with Sub-Adviser

Head of Fundamental Large Cap Growth Team, Managing Director Since 2015

Lawrence G. Kemp, CFA BlackRock Investment

Management, LLC

Managing Director and Portfolio Manager Since 2015

Patrick S. Kaser, CFA Brandywine Global Investment

Management, LLC

Managing Director and Portfolio Manager Since 2015

Paul R. Lesutis, CFA

James J. Clarke

SEI INSTITUTIONAL MANAGED TRUST

Large Cap Fund Large Cap Value Fund Large Cap Growth Fund Tax-Managed Large Cap Fund

S&P 500 Index Fund Small Cap Fund Small Cap Value Fund Small Cap Growth Fund Tax-Managed Small/Mid Cap Fund

Mid Cap Fund

U.S. Managed Volatility Fund

Global Managed Volatility Fund Tax-Managed Managed Volatility Fund

Real Estate Fund Enhanced Income Fund Core Fixed Income Fund

U.S. Fixed Income Fund High Yield Bond Fund

Real Return Fund Multi-Strategy Alternative Fund

Long/Short Alternative Fund

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In addition, under the heading “Large Cap Fund,” under the sub-section entitled Advisers and Portfolio Managers,” under the section titled “Sub-Advisers,” the text relating to AJO, LP, Brown Advisory, LLC and Waddell & Reed Investment Management Co is hereby deleted and replaced with the following text in the appropriate alphabetical order thereof:

BlackRock Investment Management, LLC: BlackRock Investment Management, LLC (BIM), located at 1 University Square Drive, Princeton, New Jersey 08540, serves as a Sub-Adviser to the Large Cap Fund. Lawrence G. Kemp, CFA manages the portion of the Large Cap Fund’s assets allocated to BIM. Mr. Kemp has served as the Head of the Fundamental Large Cap Growth Team and Managing Director of BIM since January 2013. Prior to joining BIM, Mr. Kemp served as a portfolio manager at UBS Global Asset Management since 1992, and has more than 25 years of experience in the financial industry.

Brandywine Global Investment Management, LLC: Brandywine Global Investment Management, LLC (Brandywine Global), located at 2929 Arch Street, 8th Floor, Philadelphia, Pennsylvania 19104, serves as a Sub-Adviser to the Large Cap Fund. A team of investment professionals manages the portion of the Large Cap Fund’s assets allocated to Brandywine Global. The team consists of Patrick S. Kaser, CFA, Brandywine Global’s Managing Director and Portfolio Manager, who is responsible for researching the financial and healthcare sectors, contributing insights and stock

recommendations; Paul R. Lesutis, CFA, Brandywine Global’s Managing Director and Portfolio Manager, who is responsible for general research coverage, contributing insights and stock recommendations; and James J. Clarke, Brandywine Global’s Portfolio Manager. Mr. Kaser has been with Brandywine Global since 1998. Mr. Lesutis has been with Brandywine Global since 1991. Mr. Clarke has been with Brandywine Global since December 2008. Immediately prior to joining Brandywine Global, he served as founding partner of Clarke Bennitt, LLC and co-portfolio manager of the concentrated, all-cap Montchanin funds from 2005 to 2008.

Coho Partners, Ltd.: Coho Partners, Ltd. (Coho), located at 300 Berwyn Park, 801 Cassatt Road, Suite 100, Berwyn, Pennsylvania 19312, serves as a Sub-Adviser to a portion of the assets of the Large Cap Fund. A team of investment professionals manages the portion of the Large Cap Fund’s assets allocated to Coho. Peter A. Thompson graduated from Princeton University, with a Bachelor of Arts Degree in Economics, and received his MBA from the University of Virginia’s Colgate Darden School of Business Administration. Mr. Thompson joined Kidder, Peabody & Company in 1983. His career moved from sales to research and ultimately to a position of oversight on the Stock Selection Committee and Investment Policy Committee for the firm. In 1989, Mr. Thompson joined the investment-counseling firm of Cooke & Bieler where he oversaw a wide range of research and portfolio responsibilities. In addition to managing stand-alone, separate account portfolios, he played an integral role in the development of three of the firm’s mutual funds for which he was also a portfolio manager. In 1999, Mr. Thompson founded Coho Partners, Ltd. where he is a partner, the chief

investment officer and serves on the firm’s Investment Committee. Brian L. Kramp, CFA, graduated from Muhlenberg College with a Bachelor of Arts Degree in Business Administration and Accounting. He began his investment career as a financial advisor for a regional brokerage firm in Allentown, PA in 1983. Mr. Kramp joined Meridian Bank as a personal trust investment officer in 1985, where he focused on managing individual and institutional accounts. In 1987, he progressed to analyst/portfolio manager for Meridian Investment Company, managing or co-managing several equity funds. Mr. Kramp joined Miller, Anderson, and Sherrerd/Morgan Stanley in 1997 in the role of analyst/portfolio manager. He rose to the position of executive director and enjoyed significant responsibilities at senior levels of portfolio management, equity research and client service on the large cap core and value equity teams. Mr. Kramp joined Coho Partners, Ltd. in June, 2006, where he is a partner, a portfolio manager and research analyst. He serves on the firm’s Investment Committee.

Parametric Portfolio Associates LLC: Parametric Portfolio Associates LLC (Parametric), located at 1918 Eighth Avenue, Suite 3100, Seattle, Washington 98101, serves as a Sub-Adviser to the Large Cap Fund. A team of investment professionals at Parametric, led by Paul Bouchey, Co-Chief Investment Officer—Seattle Investment Center, and Thomas Seto, Head of Investment Management—Seattle Investment Center, manages the portion of the Large Cap Fund’s assets allocated to Parametric. Messrs. Bouchey and Seto have been with Parametric since 2006 and 1998, respectively. Snow Capital Management, L.P.: Snow Capital Management, L.P. (SCM), located at 2000 Georgetowne Drive, Suite 200, Sewickley, Pennsylvania 15143, serves as a Sub-Adviser to the Large Cap Fund. A team of investment professionals manages the portion of the Large Cap Fund’s assets

Partner, CIO Since 2015

Peter A. Thompson Coho Partners, Ltd.

Partner, Portfolio Manager & Research Analyst

Since 2015 Brian L. Kramp, CFA

Co-Chief Investment Officer—Seattle Investment Center

Since 2015 Paul Bouchey

Chief Investment Officer, Principal Since 2015

Richard Snow Snow Capital Management, L.P.

Senior Portfolio Manager, Principal Since 2015

Joshua Schachter, CFA

Nathan Snyder, CFA

Portfolio Manager, Principal Since 2015

Anne Wickland, CFA

Jessica Bemer, CFA

Simon Rosenberg, CFA

Senior Analyst Since 2015

Joseph Famoso, CFA

Analyst Since 2015

Joseph Artuso, CFA

Merrill Corp - SEI Institutional Managed Trust Class A Prospectus Supplement [Funds] 033-09504 07-17-2...ED [AUX] | bjasper | 17-Jul-15 10:36 | 15-15840-2.ba

| Sequence: 2

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allocated to SCM. Richard Snow is the Chief Investment Officer and Principal at SCM, and has been with the firm since its inception in 2001. Joshua Schachter, CFA is a Senior Portfolio Manager and Principal at SCM, and has been with the firm since its inception in 2001. Nathan Snyder, CFA is a Senior Portfolio Manager and Principal at SCM, and has been with the firm since 2005. Anne Wickland, CFA is a Portfolio Manager and Principal at SCM. She joined the firm in 2006 as a Senior Analyst, and was appointed to her current role in 2010. Jessica Bemer, CFA is a Portfolio Manager and Principal at SCM. She joined the firm in 2006 as a Senior Analyst, and was appointed to her current role in 2014. Simon Rosenberg, CFA and CPA joined SCM in 2007 as a Senior Analyst, and was appointed to his current role in 2011. Joseph Famaso, CFA joined the firm in 2012 as a Senior Analyst. Joseph Artuso, CFA joined the firm in 2005 as an intern, and was appointed to his current role in 2010.

There are no other changes to the principal investment strategies or portfolio management of the Large Cap Fund. Changes to the Large Cap Value Fund’s Principal Investment Strategies and Sub-Advisers

The Large Cap Value Fund’s “Principal Investment Strategies” section is hereby deleted and replaced with the following:

Under normal circumstances, the Large Cap Value Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large companies. The Fund will primarily seek to purchase securities believed to be attractively valued in relation to various measures which may include earnings, capital structure or return on invested capital. For purposes of this Fund, a large company is a company with a market capitalization in the range of companies in the Russell 1000 Value Index (between $275 million and $391 billion as of December 31, 2014) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Value Index are subject to change. These securities may include common stocks, preferred stocks, warrants, American depository receipts (ADRs) and exchange-traded funds (ETFs). The Fund may also, to a lesser extent, invest in common and preferred stocks of small capitalization companies. The Fund may invest up to 20% of its assets in foreign securities.

The Fund uses a multi-manager approach, relying primarily on a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies and strategies to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation, the Fund’s adviser (SIMC or the Adviser). Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. In managing its portion of the Fund’s assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.

In the chart under the heading “Sub-Advisers and Portfolio Managers,” in the Fund Summary for the Large Cap Value Fund, the text relating to Lazard Asset Management LLC is hereby deleted and replaced with the following text in the alphabetical order thereof:

Partner, CIO Since 2015

Peter A. Thompson Coho Partners, Ltd.

Partner, Portfolio Manager & Research Analyst

Since 2015 Brian L. Kramp, CFA

Co-Chief Investment Officer— Seattle Investment Center Since 2015

Paul Bouchey Parametric Portfolio

Associates LLC

Chief Investment Officer, Principal Since 2015

Richard Snow Snow Capital Management, L.P.

Joshua Schachter, CFA

Nathan Snyder, CFA

Anne Wickland, CFA

Jessica Bemer, CFA

Simon Rosenberg, CFA

Senior Analyst Since 2015

Joseph Famoso, CFA

Analyst Since 2015

Joseph Artuso, CFA

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