An attempt has been taken to decolorize and mineralizePonceau S (PS), a diazo dye, in aqueous solution by Fenton process. Effects of solution pH, concentrations of H2O2, Fe(II) and PS on the decolorization of PS have also been studied through batch experiments. About 90% decolorization was found under the optimal conditions [PS]: [H2O2]: [Fe(II)] = 1:12:2 and [H2O2]/[Fe(II)] = 6 at pH 2.85 in 40 minutes. The overall results revealed that mineralization was rather slower as compared with the decolorization