Photocatalytic degradation of pollutants under solar light irradiation is an economically viable process and a very promising clean wastewater treatment technology. The aim of this study is to evaluate photocatalytic degradation of Reactive Black 5 (RB5) under natural sunlight irradiation with TiO2 as photocatalyst. The effects of initial concentration of RB5, dosage of TiO2, with/without solar irradiation, with/without air sparging and pH solution were examined. The decolorization rate improved with a higher dosage of TiO2, with sunlight irradiation and air sparging, and under acidic solution. The photocatalytic process not only decolorized the RB5 but also mineralized the intermediate products completely.