Exhibit 32.2

OSI PHARMACEUTICALS, INC.

CERTIFICATION PURSUANT TO
18 U.S.C. § 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of OSI Pharmaceuticals, Inc. (the “Company”) on Form 10-K for the year ended December 31, 2009 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Pierre Legault, Executive Vice President, Chief Financial Officer and Treasurer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

     (1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

     (2) The information contained in the Report fairly presents, in all material respects, the financial condition and result of operations of the Company.

Date: February 24, 2010

/s/ Pierre Legault  

Pierre Legault 

Executive Vice President, Chief
Financial Officer and Treasurer
(Principal Financial Officer)