A 20 mg/L methylene blue (MB) aq. soln. was oxidized in the presence of Na2S2O8 and UV radiation or O-3 and H2O2. The decoloration were carried out continuously for 20 min. Samples for anal. were taken after 5, 10, 15 and 20 min. MB content before and after the advanced oxidn. processes was detd. by the UV spectrophotometric method. A higher degree of MB decompn. was obtained in the presence of sulphate radicals (96%) than hydroxyl radicals (70%) after 20 min of the process.