The rate constants for the gas-phase reactions of methyl- and ethylperoxy radicals with NO were studied at room temperature (298 +/-2 K) and 4 Torr of pressure (He buffer) by using a laser flash photolysis coupled with time-resolved negative ionization mass spectrometry technique. The alkyl peroxy radicals were generated by the reaction of corresponding alkyl radicals with excess O-2, where alkyl radicals were prepared by laser photolysis of several precursor molecules. The rate constants were determined to be k(CH3O2 + NO) = (9.9 +/- 2.1) x 10(-12) and k(C2H5O2 + NO) = (11.0 +/- 0.8) x 10(-12) cm(3) molecule(-1) s(-1) which are about a factor of 1.3 larger than the previous recommendations.