<PAGE>

                                                                    EXHIBIT 12.2

                     CERTIFICATION PURSUANT TO SECTION 302
                       OF THE SARBANES-OXLEY ACT OF 2002

     I, Lawrence Rosen, certify that:

     1.    I have reviewed this annual report on Form 20-F of Fresenius Medical
           Care Aktiengesellschaft (the "Report").

     2.    Based on my knowledge, this Report does not contain any untrue
           statement of a material fact or omit to state a material fact
           necessary to make the statements made, in light of the circumstances
           under which such statements were made, not misleading with respect to
           the period covered by this Report.

     3.    Based on my knowledge, the financial statements, and other financial
           information included in this Report, fairly present in all material
           respects the financial condition, results of operations and cash
           flows of the company as of, and for, the periods presented in this
           Report.

     4.    The company's other certifying officer and I am responsible for
           establishing and maintaining disclosure controls and procedures (as
           defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the
           company and have:

        a)   Designed such disclosure controls and procedures, or caused such
             disclosure controls and procedures to be designed under our
             supervision, to ensure that material information relating to the
             company, including its consolidated subsidiaries, is made known to
             us by others within those entities, particularly during the period
             in which this Report is being prepared;

        b)  Evaluated the effectiveness of the company's disclosure controls and
            procedures and presented in this Report our conclusions about the
            effectiveness of the disclosure controls and procedures, as of the
            end of the period covered by this Report based on such evaluation;
            and

        c)   Disclosed in this Report any change in the company's internal
             control over financial reporting that occurred during the period
             covered by the annual report that has materially affected, or is
             reasonably likely to materially affect, the company's internal
             control over financial reporting.

     5.    The company's other certifying officer and I have disclosed, based on
           our most recent evaluation of internal control over financial
           reporting, to the company's auditors and the audit committee of the
           company's board of directors (or persons performing the equivalent
           functions):

        a)   All significant deficiencies and material weaknesses in the design
             or operation of internal control over financial reporting which are
             reasonably likely to adversely affect the company's ability to
             record, process, summarize and report financial information; and

        b)  Any fraud, whether or not material, that involves management or
            other employees who have a significant role in the company's
            internal control over financial reporting.

Date: March 1, 2005

                                          /s/ LAWRENCE ROSEN
                                          --------------------------------------
                                          Lawrence Rosen
                                          Chief Financial Officer