Exhibit 32.1

CERTIFICATION PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

(18 U.S.C. SECTION 1350)

In connection with the Annual Report of Pharmacyclics, Inc., a Delaware corporation (the “Company”), on Form 10-K for the year ended December 31, 2014 as filed with the Securities and Exchange Commission (the “Report”), I, Robert W. Duggan, Chairman of the Board and Chief Executive Officer of the Company, certify, pursuant to §906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. §1350), that to my knowledge:

(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/ ROBERT W. DUGGAN

Robert W. Duggan

Chairman of the Board and Chief Executive Officer

(Principal Executive Officer)

February 18, 2015

CERTIFICATION PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

(18 U.S.C. SECTION 1350)

In connection with the Annual Report of Pharmacyclics, Inc, a Delaware corporation (the “Company”), on Form 10-K for the year ended December 31, 2014 as filed with the Securities and Exchange Commission (the “Report”), I, Manmeet S. Soni, Principal Financial Officer of the Company, certify, pursuant to §906 of the Sarbanes-Oxley Act of 2002 (18 U.S.C. §1350), that to my knowledge:

(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/ MANMEET S. SONI

Manmeet S. Soni

Chief Financial Officer and Treasurer

(Principal Financial and Accounting Officer)

February 18, 2015