Photocatalytic degradation of five azo dyestuff by H 2O 2 and TiO 2 were studied under the high pressure mercury lamp,UV lamp and sunlight H 2O 2 and TiO 2 had a significant photocatalytic decolorizing effect on these dyes When the dyes pH was 3 or 9, concentrations of H 2O 2and TiO 2 were 0 4% and 0 25%,they showed the highest decolorizing rate The decolorizing effect of TiO 2 was better than that of H 2O 2 The mix catalytic showed a even better decolorizing effect The reaction of photo catalytic degradation was first order reaction in kinetics There was a positive relationship between remove ratio of COD and decolorizing ratio