Abstract: The uniform, transparent anatase Sn-doped TiO₂ composite thin films deposited on glass substrates were prepared by sol-gel processing. Sn-doped TiO₂ films were composed of TiO₂ sphere particles in size of 50~100 nm. The thickness of TiO₂ films prepared by 1 cycle (from dipping to teat-treatment at 500℃,1 h) is 0.09 μm or so. Anatase TiO₂ films show some orientation effect in (101) peak. XPS results have showed that besides Ti, O and Sn elements in films there are a certain amount of residual carbon from the starting organometallic components and a small amount of Na and Ca elements diffused from the glass substrates. Photo-catalytic degradation of Methyl orange aqueous solution has indicated that the sol-gel derived Sn-doped TiO₂ films show good photo-catalytic activity, and its apparent degradation rate constant k is larger than that of un-doped TiO₂ films. These results are explained on the basis of the principle of charge separation in an SnO₂/TiO₂ composite semiconductor system.