TiO 2 thin film electrode was prepared by a sol gel method on ITO substrates. Cyclic voltammetric behavior of the ITO/TiO 2 electrode under ultraviolet (UV) illumination was investigated in the solution of Na 2SO 4. There are two photoelectrochemical processes for TiO 2 electrode under UV illumination. One is a fast process, which results in the appearance of anodic photocurrent. The anodic photocurrent will appear and disappear with the light on and off. The other is a slow process, which will be responsible for the appearance of an oxidative peak. When the electrode is illuminated under UV light for a long time, a new oxidative peak can be observed. The peak current increases with the increase of UV illumination time. It is assumed that the new peak belongs to the oxidation of Ti 3+ , which formed and accumulated on the electrode surface during the UV illumination. A detailed mechanism is proposed on the base of these two photoelectrochemical processes. It is assumed that the change of hydrophilicity of TiO 2 thin film may be related to the slow process while the film irradiated by UV light. TiO 2 thin film electrode was prepared by a sol gel method on ITO substrates. Cyclic voltammetric behavior of the ITO / TiO 2 electrode under ultraviolet (UV) illumination was investigated in the solution of Na 2 SO 4. There are two photoelectrochemical processes for TiO 2 One under a fast process, which results in the appearance of anodic photocurrent. The anodic photocurrent will appear and disappear with the light on and off. When the electrode is illuminated under UV light for a long time, a new oxidative peak can be observed. It is assumed that the new peak belongs to the oxidation of Ti 3 +, which formed and accumulated on the electrode surface during the UV illumination. It is assumed that the change of hydrophilicity of TiO 2 thin film may be related to the slow process while the film irradiated by UV light.