Abstract: The photodegradation decoloring efficiencies of Nanometer TiO₂ (a kind of photocatalyst) to dyeing wastewater containing water soluble dyes (Reactive Yellow X6G, Reactive Red X3B, Reactive Blue XBR, Alkali Green, Alkali Violet and Alkali Fuchsin) have been studied. The results of the study showed that in pH 2 acidic medium the decoloring efficiencies of Nanometer TiO₂ to the six dyestuff solutions (60 mg/L) were all exceeding 93.3%. Even to the high concentration Reactive Blue solution (200 mg/L) the decoloring rate could still be as high as 78.8%. It was also concluded that the pH value of dyestuff solution has a significant influence to the decoloring function of Nanometer TiO₂.