As filed with the U.S. Securities and Exchange Commission on January 11, 2019

Securities Act File No. 33-49552

Investment Company Act File No. 811-6740

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	☒
Pre-Effective Amendment No.
Post-Effective Amendment No. 128	☒

and/or

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940 ☒

Amendment No. 134

Legg Mason Partners Institutional Trust*

(Exact Name of Registrant as Specified in Charter)

620 Eighth Avenue

New York, NY 10018

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code: (877) 721-1926

Name and address of agent for service:		Copy to:
ROBERT I. FRENKEL Legg Mason Partners Institutional Trust 100 First Stamford Place Stamford, Connecticut 06902		ROGER P. JOSEPH, ESQ. Morgan, Lewis & Bockius LLP One Federal Street Boston, Massachusetts 02110
	Continuous (Approximate Date of Proposed Offering)

It is proposed that this filing will become effective:

☒ immediately upon filing pursuant to paragraph (b)

☐ on                     pursuant to paragraph (b)

☐ 60 days after filing pursuant to paragraph (a)(1)

☐ on                     pursuant to paragraph (a)(1)

☐ 75 days after filing pursuant to paragraph (a)(2)

☐ on                     pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

☐ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

* This filing relates solely to Western Asset Institutional Government Reserves, Western Asset Institutional Liquid Reserves, Western Asset Institutional U.S. Treasury Obligations Money Market Fund, Western Asset Institutional U.S. Treasury Reserves and Western Asset Select Tax Free Reserves.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended (the “Securities Act”), and the Investment Company Act of 1940, as amended, the Registrant, LEGG MASON PARTNERS INSTITUTIONAL TRUST, hereby certifies that it meets all requirements for effectiveness of this Post-Effective Amendment to the Registration Statement pursuant to Rule 485(b) under the Securities Act and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Baltimore, State of Maryland on this 11th day of January, 2019.

LEGG MASON PARTNERS INSTITUTIONAL TRUST, on behalf of its series:

Western Asset Institutional Government Reserves

Western Asset Institutional Liquid Reserves

Western Asset Institutional U.S. Treasury

   Obligations Money Market Fund

Western Asset Institutional U.S. Treasury Reserves

Western Asset Select Tax Free Reserves

By:	/s/ Jane Trust
	Jane Trust
	President and Chief Executive Officer

WITNESS our hands on the date set forth below.

Pursuant to the requirements of the Securities Act, this Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities indicated below on January 11, 2019.

Signature	Title
/s/ Jane Trust	President, Chief Executive Officer and Trustee
Jane Trust
/s/ Richard F. Sennett	Principal Financial Officer
Richard F. Sennett
/s/ Elliott J. Berv*	Trustee
Elliott J. Berv
/s/ Jane F. Dasher*	Trustee
Jane F. Dasher
/s/ Mark T. Finn*	Trustee
Mark T. Finn
/s/ Stephen R. Gross*	Trustee
Stephen R. Gross

/s/ Richard E. Hanson, Jr.*	Trustee
Richard E. Hanson, Jr.
/s/ Susan M. Heilbron*	Trustee
Susan M. Heilbron
/s/ Susan B. Kerley*	Trustee
Susan B. Kerley
/s/ R. Richardson Pettit*	Trustee
R. Richardson Pettit
*By: /s/ Jane Trust
Jane Trust

* Attorney-in-Fact, pursuant to Power of Attorney.

SIGNATURES

Master Portfolio Trust has duly caused this Post-Effective Amendment to the Registration Statement on Form N-1A of Legg Mason Partners Institutional Trust to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Baltimore, State of Maryland on this 11th day of January, 2019.

MASTER PORTFOLIO TRUST, on behalf of its series:

Government Portfolio

Liquid Reserves Portfolio

Tax Free Reserves Portfolio

U.S. Treasury Reserves Portfolio

U.S. Treasury Obligations Portfolio

By:	/s/ Jane Trust
	Jane Trust
	President and Chief Executive Officer

WITNESS our hands on the date set forth below.

This Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities indicated below on January 11, 2019.

Signature	Title
/s/ Jane Trust Jane Trust	President, Chief Executive Officer and Trustee
/s/ Richard F. Sennett Richard F. Sennett	Principal Financial Officer
/s/ Elliott J. Berv* Elliott J. Berv	Trustee
/s/ Jane F. Dasher* Jane F. Dasher	Trustee
/s/ Mark T. Finn* Mark T. Finn	Trustee
/s/ Stephen R. Gross* Stephen R. Gross	Trustee
/s/ Richard E. Hanson, Jr.* Richard E. Hanson, Jr.	Trustee
/s/ Susan M. Heilbron* Susan M. Heilbron	Trustee

/s/ Susan B. Kerley* Susan B. Kerley	Trustee
/s/ R. Richardson Pettit* R. Richardson Pettit	Trustee
*By: /s/ Jane Trust
Jane Trust

* Attorney-in-Fact, pursuant to Power of Attorney.

EXHIBIT INDEX

Index No.	Description of Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase