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, 2006 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Michael G. Atieh, Executive Vice President and Chief Financial Officer 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.

/s/ MICHAEL G. ATIEH

Michael G. Atieh

Executive Vice President and Chief

Financial Officer

Date: February 28, 2007

129