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Prospectus Date

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May 23, 2012

Emerging Markets External Debt Portfolio (Prospectus Summary): | Emerging Markets External Debt Portfolio

Risk/Return:

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Risk/Return, Heading

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Emerging Markets External Debt Portfolio  

Supplement Text

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Prospectus Supplement

September 6, 2012

Morgan Stanley Institutional Fund, Inc.

Supplement dated September 6, 2012 to the Morgan Stanley Institutional Fund, Inc. Prospectus dated May 23, 2012 of:

Emerging Markets External Debt Portfolio

The stockholders of the Emerging Markets External Debt Portfolio (the "Portfolio") have approved a proposal to change the Portfolio's classification from a diversified fund to a non-diversified fund. Accordingly, effective immediately, the Prospectus is revised as follows:

Risk, Heading

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The following is hereby added after the ninth paragraph in the section of the Prospectus entitled "Portfolio Summary—Principal Risks":  

Risk, Narrative

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• Non-Diversified Risk. Because the Portfolio is non-diversified, it may be more susceptible to an adverse event affecting a portfolio investment than a diversified portfolio and a decline in the value of that instrument would cause the Portfolio's overall value to decline to a greater degree.

Supplement Closing

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Please retain this supplement for future reference.