EXHIBIT 31.1


                             CERTIFICATE PURSUANT TO
               RULE 13a-14 OF THE SECURITIES EXCHANGE ACT OF 1934

I, Carl E. Berg, certify that:

1.  I have  reviewed  this  Quarterly  Report  on  Form  10-Q  of  Mission  West
Properties, Inc. (the "Company") for the quarter ended March 31, 2005;

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

4.  The  Company'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-14(e)) and internal  control over financial
reporting (as defined in Exchange Act Rules 13a-15(f)) for the Company 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
          Company, 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)   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 Company's  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  quarterly  report  based on
          such evaluation; and
     d)   disclosed  in  this  quarterly  report  any  change  in the  Company's
          internal  control over financial  reporting  that occurred  during the
          Company's  first fiscal  quarter that has materially  affected,  or is
          reasonably likely to materially affect, the Company's internal control
          over financial reporting; and

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


Carl E. Berg
Chairman and Chief Executive Officer
May 9, 2005