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 โข5H 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 TiO 2 and Sn 0.05 Ti 0.95 O 2 samples if calcining temperature is below 500 โ. The rutile phase has appeared and coexisted with the anatase crystal phase for both pure TiO 2 and Sn 0.05 Ti 0.95 O 2 composite oxides when calcining was at 600 โ. Transmission electron microscopy analysis shows a smaller grain size in Sn 0.05 Ti 0.95 O 2 powders than TiO 2 powders calcined at 600 โ. When calcining temperature is 700 โ, there is only rutile phase in Sn 0.05 Ti 0.95 O 2 samples, but there are still two crystal phases, anatase and rutile, coexisting in the pure TiO 2 samples. Assuming the grain growth obeys the first order kinetics, Arrhenius empirical relation has been used to estimate the activation energy of 47.486 and 33.103 kJโขmol -1 for the grain growth of TiO 2 and Sn 0.05 Ti 0.95 O 2 , respectively. The photo-catalytic activity of the powder samples has been examined by measuring the degradation of methylene blue solution under ultra-violet irradiation. Two effective factors of photo-catalytic activity namely, the content of SnO 2 in the TiO 2 samples and the calcining temperature, have been optimized based on the photo-catalytic degradation of methylene blue solution.