Exhibit 31.1
 CERTIFICATION PURSUANT TO
RULES 13a-14(a) AND 15d-14(a) UNDER THE SECURITIES
EXCHANGE ACT OF 1934, AS AMENDED
  1.
    
    I have reviewed this quarterly report on Form 10-Q of Brandywine Realty Trust: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 in 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(s) and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in Exchange
Act Rules 13a-15(e) and 15(d)-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 other 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 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; andd.
    
    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 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):




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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; andb.
    
    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 8, 2009
    /s/ Gerard H. SweeneyGerard H. SweeneyPresident and Chief Executive Officer