EXHIBIT NO. 99.(a)8

MFS SERIES TRUST IX

CERTIFICATION OF AMENDMENT

TO THE DECLARATION OF TRUST

REDESIGNATION OF CLASS R3 SHARES, CLASS R4 SHARES, AND

CLASS R5 SHARES

Pursuant to Sections 6.10 and 9.3 of the Amended and Restated Declaration of Trust dated December 16, 2004, as amended (the “Declaration”), of MFS Series Trust IX, a business trust organized under the laws of The Commonwealth of Massachusetts (the “Trust”), the undersigned Trustees of the Trust, being a majority of the Trustees of the Trust, do hereby redesignate all existing Class R3, Class R4, and Class R5 shares (as defined in the Declaration) of MFS Bond Fund, MFS Inflation-Adjusted Bond Fund, MFS Limited Maturity Fund and MFS Research Bond Fund, each a series of the Trust, as follows:

The class of shares previously designated as “Class R3 Shares” shall be redesignated as “Class R2 Shares,” the class of shares previously designated as “Class R4 Shares” shall be redesignated as “Class R3 Shares,” and the class of shares previously designated as “Class R5 Shares” shall be redesignated as “Class R4 Shares.”

IN WITNESS WHEREOF, a majority of the Trustees of the Trust have executed this amendment, in one or more counterparts, all constituting a single instrument, as an instrument under seal in The Commonwealth of Massachusetts, as of April 22, 2008, and further certify, as provided by the provisions of Section 9.3(c) of the Declaration, that this amendment was duly adopted by the undersigned in accordance with Section 9.3(a) of the Declaration.

ROBERT E. BUTLER	ROBERT J. MANNING
Robert E. Butler 804 W. Park Avenue State College PA 16803	Robert J. Manning 13 Rockyledge Road Swampscott MA 01907
LAWRENCE H. COHN	LAWRENCE T. PERERA
Lawrence H. Cohn 45 Singletree Road Chestnut Hill MA 02467	Lawrence T. Perera 18 Marlborough Street Boston MA 02116
DAVID H. GUNNING	ROBERT C. POZEN
David H. Gunning 2571 N. Park Blvd. Cleveland Heights OH 44106	Robert C. Pozen 9 Arlington Street Boston MA 02116
WILLIAM R. GUTOW	J. DALE SHERRATT
William R. Gutow 3 Rue Dulac Dallas TX 75230	J. Dale Sherratt 86 Farm Road Sherborn MA 01770
MICHAEL HEGARTY	LAURIE J. THOMSEN
Michael Hegarty 177 Old Briarcliff Road Briarcliff Manor NY 10510	Laurie J. Thomsen 235 Nashawtuc Road Concord MA 01742
J. ATWOOD IVES	ROBERT W. UEK
J. Atwood Ives 17 West Cedar Street Boston MA 02108	Robert W. Uek 536 Tierra Mar Lane Naples FL 34108