p-n Junction photocatalyst NiO/TiO2 was prepared by sol-gel method using Ni(NO3)(2)center dot 6H(2)O and tetrabutyl titanate [Ti(OC4H9)(4)] as the raw materials. The p-n junction photocatalyst NiO/TiO2 was characterized by UV-vis diffuse reflection spectrum, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr2O72- and photocatalytic oxidation of rhodamine B. The results show that, for photocatalytic reduction of Cr2O72-, the optimum percentage of doped-NiO is 0.5% (mole ratio of Ni/Ti). The photocatalytic activity of the p-n junction NiO/TiO2 is much higher than that of TiO2 on the photocatalytic reduction of Cr2O72-. However, the photocatalytic activity of the p-n junction photocatalyst NiO/TiO2 is much lower than that of TiO2 on the photocatalytic oxidation of rhodamine B. Namely, the p-n junction photocatalyst NiO/TiO2 has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. Effects of heat treatment on the photocatalytic activity of p-n junction photocatalyst NiO/TiO2 were investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p-n junction principle. (C) 2007 Elsevier B.V. All rights reserved.