TiO2 nano powder doping with Sn4+ was directly synthesized by a low temperature hydrothermal method using tetrabutyl titanate (TBOT) as a Ti resource and NH4Cl as a dispersant. The synthesized nano powder was characterized by XRD, BET, TEM and EDS analyses. XRD results show that increasing reaction temperature facilitates to form a stable phase, and the synthesized nano power size is uniform with particle size of 10-20 nm. Doping Sn4+ ion does not result in an obvious lattice distortion. The effect of doping Sn4+ ion on photocatalytic activity in visible light region for modified TiO2 was investigated by degrading methylene blue solution.