File Nos. 333-90789

811-09685

As filed with the Securities and Exchange Commission on March 10, 2014

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER
THE SECURITIES ACT OF 1933	x
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 26	x

and/or

REGISTRATION STATEMENT

UNDER
THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 27	x

(Check appropriate box or boxes)

PIONEER HIGH YIELD FUND

(Exact Name of Registrant as Specified in Charter)

60 State Street, Boston, Massachusetts 02109

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code: (617) 742-7825

Terrence J. Cullen, Pioneer Investment Management, Inc.,

60 State Street, Boston, Massachusetts 02109

(Name and Address of Agent for Service)

It is proposed that this filing will become effective (check appropriate box):

x immediately upon filing pursuant to paragraph (b)

¨ on [date] pursuant to paragraph (b)

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

¨ on [date] pursuant to paragraph (a)(1)

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

¨ on [date] 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.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Fund certifies that it meets all of the requirements for effectiveness of this registration statement under Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No. 26 to its Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of Boston and The Commonwealth of Massachusetts on the 10th day of March, 2014.

	PIONEER HIGH YIELD FUND
By:	/s/ Daniel K. Kingsbury
	Daniel K. Kingsbury
	President

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities indicated below on March 10, 2014:

	Signature	Title
	Mark E. Bradley*	Treasurer (Principal Financial and Accounting Officer)
	Mark E. Bradley
	David R. Bock*	Trustee
	David R. Bock
	Benjamin M. Friedman*	Trustee
	Benjamin M. Friedman
	Margaret B. W. Graham*	Trustee
	Margaret B. W. Graham
	/s/ Daniel K. Kingsbury	President (Principal Executive Officer) and Trustee
	Daniel K. Kingsbury
	Marc O. Mayer*	Trustee
	Marc O. Mayer
	Thomas J. Perna*	Chairman of the Board and Trustee
	Thomas J. Perna
	Marguerite A. Piret*	Trustee
	Marguerite A. Piret
	Kenneth J. Taubes*	Trustee
	Kenneth J. Taubes
	Stephen K. West*	Trustee
	Stephen K. West
*By:	/s/ Daniel K. Kingsbury	Dated: March 10, 2014
	Daniel K. Kingsbury
	Attorney-in-fact

EXHIBIT INDEX

Index Number	Description of Index
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Document
EX-101.DEF	XBRL Taxonomy Extension Definition Document
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase