Nano TiO 2 powders with pure anatase structure were prepared by the method of precipitation solution gelation, using H 2TiO 3, hydrogen peroxide and ammonia as reactants. Active red X 3B dye solution was selected as a model pollutant for the photocatalysis degradation experiments. The effects of grain sizes, dosage and microstructure of nano TiO 2 on its photocatalysis properties were studied. The results show that photo activity of the nano TiO 2 is enhanced with the grain sizes reducing or dosages increasing of nano TiO 2. However, excess increase in nano TiO 2 concentration is not advantageous to the enhancement of the photo activity. Anatase TiO 2 demonstrated a higher photo activity than rutile TiO 2. The dye solution hardly degraded without nano TiO 2 powders being added into it or under sunlight irradiation. Nano TiO 2 powders with pure anatase structure were prepared by the method of precipitation solution gelation, using H 2 TiO 3, hydrogen peroxide and ammonia as reactants. Active red X 3B dye solution was selected as a model pollutant for the photocatalysis degradation experiments. The effects of grain sizes, dosage and microstructure of nano TiO 2 on its photocatalysis properties were studied. The results show that photo activity of the nano TiO 2 is enhanced with the grain sizes reducing or dosages increasing of nano TiO 2. However, excess increase in nano TiO 2 concentration is not advantageous to enhance the photo activity. Anatase TiO 2 demonstrated a higher photo activity than rutile TiO 2. The dye solution was hardly degraded without nano TiO 2 powders being added into it or under sunlight irradiation.