<PAGE>

                                                                    Exhibit 31.2

                                 CERTIFICATIONS

I, Anthony Principe, certify that:

1. I have reviewed this annual report on Form 10-K of On2 Technologies, Inc. ;

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

  4. The registrant'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 control over financial
reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the
registrant 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
         registrant, 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) 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 the registrant'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

         (d) Disclosed in this report any change in the registrant's internal
         control over financial reporting that occurred during the registrant's
         most recent fiscal quarter (the registrant's fourth fiscal quarter in
         the case of an annual report) that has materially affected, or is
         reasonably likely to materially affect, the registrant's internal
         control over financial reporting; and

  5. The registrant's other certifying officer and I have disclosed, based on
our most recent evaluation of internal control over financial reporting, to the
registrant's auditors and the audit committee of the registrant'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 registrant'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 registrant's
         internal control over financial reporting.

Date: March 15, 2006


                                             By:  /s/ ANTHONY PRINCIPE
                                                 -----------------------
                                                 Anthony Principe
                                                 Chief Financial Officer