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Exhibit 31.2 CERTIFICATION
Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 I, Harry Brill, certify that: 
 1. I have reviewed this annual report on
Form 10-K as amended by Amendment No. 2 to Form 10-K of Gladstone Commercial Corporation; 
 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 annual 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
15d-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 we 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 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; and d) disclosed in this report any changes 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 registrants board of directors (or persons performing the equivalent
functions): a) all significant deficiencies and material weaknesses in the design or operation of internal
controls over financial reporting which are reasonably likely to adversely affect the registrant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 registrants internal control over financial reporting. 
 Date: October 19, 2005 
 /s/ HARRY BRILL
Harry Brill
Chief Financial Officer and Treasurer 5