PEG6000-OSO3H was prepared and was characterized by FT-IR, TG and element analysis. Baeyer-Villiger oxidation of ketones catalyzed by PEG6000-OSO3H with 30%H2O2 as oxidant was studied. The influences of the solvents, the reaction time, the temperature, the dosage of catalyst and the oxidant on the catalytic activity are well investigated. The optimizing conditions were concluded as: 0.1mmol of ketones could be well oxidized with 3.0eq of 30 %H2O2 catalyzed by 10 mg of PEG6000-OSO3H in 3mL of acetonitrile at 70 oC for 24 hours. Under the optimum condition, a series of cyclic ketones such as 2-adamantanone, cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 4-methylcyclohexanone and 4-tert-butylcyclohexanone were well transformed into the corresponding lactones with the conversion of 89%～100% and the selectivity of 89%～99%, respectively. Some of the products of lactones from the oxidations were purified by a silica gel column and characterized by 1H NMR and 13C NMR spectra.