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                                                                    EXHIBIT 31.2

                            SECTION 302 CERTIFICATION

I, Robert J. Chamberlain, 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 14, 2006                                   /s/ ROBERT J. CHAMBERLAIN
                                                       -------------------------
                                                         Robert J. Chamberlain
                                                         Chief Financial Officer