Exhibit 31.2 CERTIFICATION PURSUANT TO
SECTION 302 OF
THE SARBANES-OXLEY ACT OF 2002 I, Thomas J. Iacopelli certify that:  1.
    
    I have reviewed this annual report on Form 10-K of NYMAGIC, INC.;  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 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 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 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 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
control 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. March 12, 2010
    
    /s/ Thomas J. IacopelliThomas J. IacopelliChief Financial Officer
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