TiO₂thin films were deposited by ion beam assisted electron beam evaporation and annealed at 200, 300, 400 and 500 ¡æ in air for one hour. The crystal structures and morphology of the samples were analyzed by an X-ray diffractometer and an atomic force microscope. The transmittance spectra were recorded by a UV-visible spectrophotometer. The results show that both the as-deposited TiO₂thin film and that one annealed at 200 ¡æ are amorphous. The sample annealed at 300 ¡æ crystallizes in pure brookite phase and is preferentially oriented along the (121) plane. When the annealing temperature rises up to 400 and 500 ¡æ, TiO₂thin films turn into pure anatase phase. All the samples exhibit high transmittance in the visible region. With the increase of annealing temperature, the transmittance slightly declines and the optical bandgaps also slightly decreases.