Abstract: Nanoparticles of TiO2 were synthesized by hydrolysis of tetrabutyl titanate in a microemulsion system of CTAB/n-hexanol/water under low temperature.The particles were characterized by X-ray diffraction and TG-DSC. The photocatalytic activity was evaluated by photocatalytic degradation of methyl orange under UV and and visible light irradiation. The effects of low-temperature aging on the photocatalytic activity were discussed. The experiment of photocatalysis shows that the activity of synthesized TiO2 is better than the pure TiO2.