In this study, various transparent TiO2 films were deposited on unheated glass-slide substrates by dc reactive sputtering technique. For one set of samples the ratio of Ar to O-2 (G(R)) was varied from 9:1 to 6:4 for a fixed sputtering pressure of 0.8 Pa, while for another set of samples the total working pressure was varied from 0.2 to 0.8 Pa for a fixed G(R) of 7:3. The crystallographic and optical properties of TiO2 films were investigated in detail. The photocatalytic activity was evaluated by the measurement of decomposition of methanol under UV-visible irradiation. The structure of the TiO2 films, prepared with various G(R), varied from amorphous to different crystalline phases. Similarly sputtering pressure variation induced change of crystalline phase and crystallinity of TiO2 films. The crystallinity improved greatly with decreasing sputtering pressure. The average transmittances of all of the TiO2 films were almost constant for wavelengths in the range of 900-380 nm for G(R)-varied thin films. The optical transmission edge of the TiO2 films deposited at various sputtering pressure shifts toward low wavelength with higher sputtering pressure. The as-deposited TiO2 films successfully photocatalyzed methanol to CO2 and H2O, measured by Fourier transform infrared spectrometer. The decomposition efficiency of TiO2 films increased with increasing sputtering pressure. However, the photocatalytic efficiency of TiO2 films prepared at different G(R) did not show any regular dependence. The high photocatalytic activity of the sample prepared with G(R)=7:3 at sputtering pressure of 0.8 Pa was tried to be explained by the effect of surface morphology and pure anatase crystalline phase.