**Exhibit 31.1**

**CERTIFICATION      PURSUANT TORULES13a-14(a) AND 15d-14(a) UNDER THE SECURITIESEXCHANGEACT OF 1934, AS AMENDED**

I, Gerard H.Sweeney, certify that:

| 1.     | I        have reviewed this quarterly report on Form 10-Q of Brandywine Operating    Partnership, L.P.:                                                                                                                                                                                                                                                                       |
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| 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;                                     |
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| 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;                                                               |
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| 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: |
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|   | 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; |
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|   | 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; and |
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|   | d.                                                                                                                                                                                                                                                                                                                                                                            | 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 |
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| 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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|   |                     |                                     |
|--------|--------------------------|------------------------------------------|
|   | Date: August    12, 2005 | /s/    Gerard H. Sweeney                 |
|   |                     |                                          |
|   |                     | Gerard    H. Sweeney                     |
|   |                     | President    and Chief Executive Officer |

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