Mercer International (MERC) 10-Q 2012 Q3 Quarterly report

EXHIBIT 32.1

CERTIFICATION OF PERIODIC REPORT

I, Jimmy S.H. Lee, Chief Executive Officer of Mercer International Inc. (the “Company”), certify pursuant to Section 906 of theSarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, that:

(1) the Quarterly Report on Form 10-Q of the Company for the quarterly period ended September 30, 2012 (the “Report”) fully complies with the requirements of Section 13(a) of theSecurities Exchange Act of 1934(15 U.S.C. 78m or 78o(d)); and

(2) the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: November 2, 2012

/s/ Jimmy S.H. Lee

Jimmy S.H. Lee

Chief Executive Officer

A signed original of this written statement required by Section 906 has been provided to Mercer International Inc. and will be retained by Mercer International Inc. and furnished to the Securities and Exchange Commission or its staff upon request.