As filed with the U.S. Securities and Exchange Commission on July 13, 2018

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. 126	☒
and/or REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	☒
Amendment No. 132

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	Roger P. Joseph, Esq.
Legg Mason Partners Income Trust	Morgan, Lewis & Bockius LLP
100 First Stamford Place	One Federal Street
Stamford, Connecticut 06902	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 This filing relates solely to Western Asset SMASh Series M Fund, Western Asset SMASh Series C Fund, Western Asset SMASh Series EC Fund and Western Asset SMASh Series TF Fund.

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, certifies that it meets all of the 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 13th day of July, 2018.

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

Western Asset SMASh Series M Fund

Western Asset SMASh Series C Fund

Western Asset SMASh Series EC Fund

Western Asset SMASh Series TF Fund

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 July 13, 2018.

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.

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