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 June 30, 2005;

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 Company as of,
and for, the periods presented in this 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) and 15d-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 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 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 Company's  internal control
          over  financial  reporting  that occurred  during the  Company's  most
          recent 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
August 9, 2005