Certification of the
Chief Financial Officer under Rule 13a-14(a)  
EXHIBIT 31.2 
I, Michael D. Mulholland, certify
that: 
     
          
          |  | 1. | I have reviewed this Quarterly Report on Form 10-Q of Barrett Business Services,
          Inc.; | 
          
          
     
          
          |  | 2. | Based on my knowledge, this quarterly 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 quarterly
          report; | 
          
          
     
          
          |  | 3. | Based on my knowledge, the consolidated financial statements, and other
          financial information included in this quarterly 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 quarterly
          report; | 
          
          
     
          
          |  | 4. | The Registrants 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 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 quarterly report is being prepared; | 
          
          
     
          
          | (b) | Evaluated the effectiveness of the Registrants disclosure controls and
          procedures and presented in this quarterly 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 Registrants internal control
          over financial reporting that occurred during the Registrants most recent
          fiscal quarter that has materially affected, or is reasonably likely to
          materially affect, the Registrants internal control over financial
          reporting; and | 
          
          
     
          
          |  | 5. | The Registrants other certifying officer and I have disclosed, based on
          our most recent evaluation of internal control over financial reporting, to the
          Registrants auditors and the audit committee of the Registrants
          board of directors: | 
          
          
     
          
          | (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 Registrants 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 Registrants internal control over
          financial reporting. | 
          
          
     |  |  | 
     | 
 Dated:  November 14, 2005
 | 
 /s/ Michael D. Mulholland
 | 
     |  | Michael D. Mulholland | 
     |  | Chief Financial Officer | 
     |  |  |