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                                                                    EXHIBIT 31.2

                            SECTION 302 CERTIFICATION

I, Brian C. Henry, certify that:

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

2.    Based on my knowledge, this annual 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 annual report;

3.    Based on my knowledge, the financial statements, and other financial
      information included in this annual 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 annual 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)) and internal controls over financial
      reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for
      Onyx 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 Onyx,
            including its consolidated subsidiaries, is made known to us by
            others within those entities, particularly during the period in
            which this annual report is being prepared;

      (b)   Designed such internal control over financial reporting, or caused
            such internal control over financial reporting to be designed under
            our supervision, to provide reasonable assurance regarding the
            reliability of financial reporting and the preparation of financial
            statements for external purposes in accordance with generally
            accepted accounting principles;

      (c)   Evaluated the effectiveness of Onyx's disclosure controls and
            procedures and presented in this annual 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

      (d)   Disclosed in this report any change in the Onyx's internal control
            over financial reporting that occurred during the 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: March 24, 2005        /s/ BRIAN C. HENRY
                            ----------------------------------------------------
                            Brian C. Henry
                            Executive Vice President and Chief Financial Officer