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                                                                    EXHIBIT 31.2

           CERTIFICATION PURSUANT TO ITEM 601(b)(31) OF REGULATION S-K
                          (Principal Financial Officer)

I, Douglas C. Sandvig, certify that:

      1. I have reviewed this annual report on Form 10-K of Smithway Motor
      Xpress Corp.;

      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)) for the registrant
      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 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) 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

         c) disclosed in this report any change in the registrant's internal
      control over financial reporting (as defined in Exchange Act Rules
      13a-15(f) and 15d-15(f)) 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.

      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 28, 2006             /s/ Douglas C. Sandvig
                                 -----------------------------------------------
                                 Douglas C. Sandvig
                                 Senior Vice President,
                                 Chief Financial Officer and Treasurer