Pure and nickel doped TiO₂ thin films on soda glass substrates were prepared by sol–gel dip coating process. The resulting films were annealed at 500°C for 1h and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV–vis-near IR techniques. AFM reveals that doping of Ni ions suppresses the grain growth of crystal in the TiO₂ film. The contact angle with water of these films was measured by sessile drop method. The undoped films could be entirely wetted by water after 1h UV illuminations, while 0.5mol% Ni ion-doped films become entirely wetted after 20min UV illumination. The photo-catalytic activity was characterized by photo-catalytic degradation of aqueous methyl orange under UV radiation. It is found that, with a suitable amount (2–10mol%), the Ni dopant increases the photo-catalytic activity of TiO₂ films. The mechanism can be attributed to these processes: (1) as the anatase grain sizes decrease with Ni doping and the specific surface areas of doped TiO₂ films increase, the charge transfer in TiO₂ film is promoted; (2) by enhancing the electron–hole pair separation and inhibiting their recombination, the Ni dopant enhances the charge pair separation efficiency for doped TiO₂ films.