Thin titanium dioxide (TiO2) films were deposited by pulsed KrF excimer laser ablation deposition system using a titanium oxide target. The effects of substrate temperature and oxygen partial pressure on the phase formations of various microstructures were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman scattering spectroscopy, and UV-Vis spectrophotometer. The film structures range from amorphous to mixed phase of anatase and rutile to pure anatase. Increasing the substrate temperature improves the quality of anatase phase of crystalline TiO2 films. The oxygen pressure in the range between 15 and 60 mTorr shows a single anatase phase in TiO2 films while the rutile and anatase mixed phases were observed elsewhere. The band gap of TiO2 films varied from 2.72 to 3.27 eV with increasing oxygen partial pressure while the film structures changed from rutile phase to anatase phase. The surface area of TiO2 films increased as oxygen partial pressure in film deposition. The photocatalytic performance evaluated by degradation of methylene blue in UV light was distinguishable in the TiO2 films with high anatase phase and surface area. (C) 2008 American Vacuum Society.