The photocatalytic performance of TiO 2 thin films coated on porous alumina balls using various aqueous TiOCl 2 solutions as starting precursors, to which 1.0 mol% transition metal ( Ni 2+ ,Cr 3+ ,Fe 3+ ,Nb 3+ ,andV 5+ ) chlorides had been already added, has been investigated, together with characterizations for TiO 2 sols synthesized simultaneously in the same autoclave through hydrothermal method. The synthesized TiO 2 sols were all formed with an anatase phase, and their particle size was between several nm and 30 nm showing ζ?potential of ?25∼?35 mV, being maintained stable for over 6 months. However, the TiO 2 sol added with Cr had a much lower value of -potential and larger particle sizes. The coated TiO 2 thin films had almost the same shape and size as those of the sol. The pure TiO 2 sol showed the highest optical absorption in the ultraviolet light region, and other TiO 2 sols containing Cr 3+ ,Fe 3+ andNi 2+ showed higher optical absorption than pure sol in the visible light region. According to the experiments for removal of a gas-phase benzene, the pure TiO 2 film showed the highest photo dissociation rate in the ultraviolet light region, but in artificial sunlight the photo dissociation rate of TiO 2 coated films containing Cr 3+ ,Fe 3+ andNi 2+ was measured higher together with the increase of optical absorption by doping.