TiO2 thin films were deposited on Si wafer and glass substrates by dc magnetron sputtering with rf power applied to the substrates. Effect of the radio frequency (rf) powers ranging from 0 to 25 W on the microstructure and optical properties of the thin films was investigated in detail. Microstructure, surface morphology, and optical properties of the TiO2 thin films were characterized by glancing incidence X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy atomic force microscopy UV/visable spectrophotometry, and ellipsometry. The influence of deposition conditions of the TiO2 films on the photocatalytic activity of methylene blue under UV illumination was also examined. It was found that the microstructure and morphology of the films are dependent strongly on the rf power. The anatase phase was obtained for the films prepared at rf powers of 0 and 5 W, whereas the films exhibit a rutile phase at rf powers of 15 and 25 W. The rf-bias-assisted TiO2 films have a smoother surface than that without rf power, and the absorbance edges shift to long wavelengths. The TiO2 films with a rutile phase have a higher refractive index; nevertheless, better photocatalytical properties were observed for the films having anatase phase. (c) 2006 The Electrochemical Society.