TiO2 thin films with photocatalytic activity were deposited on microscope glass slides by means of dc magnetron sputtering. Uniform and transparent TiO2 thin films could be prepared when oxygen flow rate surpassed its threshold. The substrate temperature ran up quickly to 110℃ in the first hour and the final substrate temperature after seven hours was no more than 130℃. The film deposited for two hours was amorphous, whereas anatase crystal phase appeared in the film deposited from three to seven hours. The amorphous films and the films composed of small crystalline particles performed quantum size effects and their band edges had a blue shift compared with the well-crystallized films. The titanium in the films was in the oxidation state of Ti^4＋. The transmittance of the films decreased and the photocatalytic activity of the films increased steadily with increasing deposition time and film thickness.