Titanium dioxide thin films were deposited on stainless steel substrates by radio frequency (RF) magnetron sputtering method. The relative humidity (RH) and oxygen content of the environment were varied systematically. The hydrophilicity of the films under ultraviolet (UV) irradiation was investigated. It was found that the hydrophilicity of the films was strongly affected by the RH and the oxygen content of the environment. This would be attributable to the adsorption of oxygen and hydroxyl group and the recombination of the electron-hole pair would be affected by the adsorbed species too. In the X-ray photoelectron spectroscopy (XPS) experiment, we succeeded in measuring the effect of UV irradiation using helium light source of ultraviolet photoelectron spectroscopy (UPS). The XPS analysis revealed that under UV irradiation, Ti3+ was produced and the adsorption of hydroxyl groups on the surface of TiO2 films was increased. The titanium dioxide films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). (c) 2005 Elsevier B.V. All rights reserved.