The rate constant of the reaction OH + CH3O2 → products (R1). has been measured at 294K by simultaneous coupling of Laser Induced Fluorescence (LIF) and cw-Cavity Ring Down Spectroscopy (cw-CDRS) to laser photolysis. OH radicals were generated by 248nm photolysis of either O3 in the presence of H2O or H2O2, CH3O2 radicals were generated simultaneously by photolysis of CH3I and their absolute concentrations were obtained by cw-CRDS. OH decays were measured under excess CH3O2 concentrations and a very fast rate constant ofk1 = (2.8±1.4)×10-10cm3s-1 was found independent of pressure at 50 and 100 Torr helium.