The effect of Lanthanum content, calcinating temperature and calcinating time on the photocatalytic activity of Lanthanum doping TiO 2 was investigated. The study showed that samples treated under higher temperature and longer calcinating time exhibited higher photocatalytic activity. The X ray diffraction pattern revealed that the lattice of those samples was highly expanded. It is suggested that the highly distorted crystal lattice may be involved in producing more ways by which the hole was captured. Thus, the photocatalytic activity of samples treated under higher temperature and longer time was promoted.