Rare-earth doped porous nanocrystalline TiO2 films were prepared via sol-gel method. The effect of preparation conditions on the properties of the resulting thin films, such as structure, surface topography and photocatalysis properties was analyzed. It indicated that appropriate doping of rare-earth element improves the photocatalysis ability of the thin titanium oxide films. The thin titanium oxide films have good photocatalysis properties in visible light region because of the red shift of energy level. It also revealed that uni-doped of cobalt is better than that of cobalt and lanthanum, while co-doping of cerium, cobalt and lanthanum may cause the best photocatalysis properties.