WELLS REAL ESTATE FUND XII, L.P.



EXHIBIT 31.2

PRINCIPAL FINANCIAL OFFICER

CERTIFICATION

PURSUANT TO

SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

(18 U.S.C. 1350)

I, Douglas P.
Williams, certify that:



|1. | I have reviewed this quarterly report on Form 10-Q of the Partnership;
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|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;
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|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 Registrant as of, and for, the periods presented in this quarterly report;
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|4. | The Registrants other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange
Act Rules 13a-15e and 15d-15e 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 others within those entities, particularly during the period in which this quarterly report is being prepared;
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| | (b) | evaluated the effectiveness of the Registrant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
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| | (c) | disclosed in this quarterly report any change in the Registrants internal control over financial reporting that occurred during the Registrants most
recent fiscal quarter 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 officers and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the
Registrants auditors and the board of directors of the corporate general partner of one of the General Partners (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; and
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| | (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.
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|November 13, 2006 |  | By: |  | /s/    DOUGLAS P.
WILLIAMS                     
|                  |  |     |  | Douglas P. Williams Principal Financial Officer