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                                                                    EXHIBIT 31.2

                            SECTION 302 CERTIFICATION

I, Brian C. Henry, certify that:

1.    I have reviewed this report on Form 10-Q of Onyx Software Corporation;

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
      Onyx as of, and for, the periods presented in this report;

4.    Onyx's other certifying officer and I are responsible for establishing and
      maintaining disclosure controls and procedures (as defined in Exchange Act
      Rules 13a-15(e) and 15d-15(e)) for Onyx and we 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 Onyx,
            including it 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 Onyx'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 Onyx's internal control over
            financial reporting that occurred during Onyx's most recent fiscal
            quarter (Onyx's fourth fiscal quarter in the case of an annual
            report) that has materially affected, or is reasonably likely to
            materially affect, Onyx's internal controls over financial
            reporting; and

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

      (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 Onyx'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 Onyx's internal
            control over financial reporting.

Date: November 9, 2004

                                                 By: /s/ Brian C. Henry
                                                     ---------------------------
                                                           Brian C. Henry
                                                      Executive Vice President
                                                     and Chief Financial Officer