SnO 2 -doped TiO 2 films and composite oxide powders have been prepared by a sol-gel method. Ti(OC 4 H 9 ) 4 and SnCl 4 •5H 2 O were used as precursors and C 2 H 5 OH was used as solvent. The optical absorption measurements indicate that the composite oxide SnO 2 -TiO 2 thin films exhibit smaller optical energy band gaps than pure TiO 2 thin films and the optical energy band gap decreases as calcining temperature increases. X-ray diffraction was used to characterize the phase transition for the composite oxide powders at different calcining temperatures. Aanatase phase is the main crystal structure in both pure