The catalytic performance of various protonated zeolites for the Baeyer-Villiger (BV) oxidation of cyclopentanone to delta-valerolactone with aqueous H2O2 as an oxidant was investigated. It was found that highly siliceous HZSM-5 zeolites are active for the oxidation reaction, and that the oxidation reaction is promoted by the Bronsted acid sites in the intracrystallines of zeolites, not on the external surface. The influences of the reaction variables (solvent, temperature, and time) and the crystal size of zeolite on the conversion of cyclopentanone and the yield of delta-valerolactone were also studied.