This project consist of three parts ,the first part Synthesis of the reagent 4-(6- Nitro- 2- benzothiazolylazo) phloroglucinol [6-NO2BTAPG],. Second part include prepared sensitized antimony tri oxide catalyst using prepared reagent ( first part).In the last part employ the malachite green dye for study photo activity of sensitized antimony tri oxide . Different experiments are performed at various conditions to reach the optimum value of dye concentration and catalyst ,which include the effect of concentration malachite green, the effect of mass loaded of sensitized antimony tri oxide catalyst, and the effect of hydrogen per oxide. UV-Vis spectrophotometer has been used to investigate the products.All experiments been carried out using suspension solution of dye irradiated by 125 watts mercury lamp.