EXHIBIT 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of IMPSAT Fiber Networks on Form 10-Q for the period ending June 30, 2006, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Ricardo A. Verdaguer, Chief Executive Officer of the registrant, certify, pursuant to 18 U.S.C. 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, to the best of my knowledge, that:

1. The Report fully complies with the requirements of Section 13(a) or 15(d), as applicable, of the Securities Exchange Act of 1934; and

2. The information contained in the Report fairly presents, in all material respects, the financial condition and result of operations of the registrant.

A signed original of this written statement required by Section 906 of the Sarbanes-Oxley Act of 2002 has been provided to the registrant and will be retained by the registrant and furnished to the Securities and Exchange Commission or its staff upon request.

Date: Aug 14, 2006

/s/ RICARDO A. VERDAGUER

Ricardo A. Verdaguer

President and Chief Executive Officer

IMPSAT FIBER NETWORKS INC 10-Q