EXHIBIT 32.2

                  CERTIFICATION OF THE CHIEF FINANCIAL OFFICER
   PURSUANT TO RULE 13a-14(b) OF THE EXCHANGE ACT AND 18 U.S.C. SECTION 1350.

      In connection with the Quarterly Report on Form 10-Q of Penwest
Pharmaceuticals Co. (the "Company") for the period ended June 30, 2005 as filed
with the Securities and Exchange Commission on the date hereof (the "Report"),
the undersigned, Jennifer L. Good, Vice President, Finance and Chief Financial
Officer of the Company, hereby certifies, pursuant to 18 U.S.C. Section 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 results of operations of the
Company.

   Dated: August 5,  2005               /s/ Jennifer L. Good
                                        ---------------------------------------
                                        Jennifer L. Good
                                        Senior Vice President, Finance and
                                        Chief Financial Officer

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