<PAGE>

                                                                    EXHIBIT 31.2

                                  CERTIFICATION

I, Greg B. Spear, certify that:

1.    I have reviewed this amended annual report on Form 10-K/A of Columbia
      Bancorp;

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

3.    Based on my knowledge, the financial statements, and other financial
      information included in this amended annual 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
      amended annual report;

4.    The registrant's other certifying officer(s) 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 amended 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 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 amended annual 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 amended 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(s) 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:  May 6, 2005                      /s/ GREG B. SPEAR
                                              -----------------
                                              Greg B. Spear
                                              Chief Financial Officer and Chief
                                              Accounting Officer

                                       9