In this paper, p-type ZnO powder was prepared by decomposition of zinc nitrate at 350 degrees C for 1 h. p-n junction photocatalyst p-ZnO/TiO2 was prepared by ball milling of TiO2 in H2O solution doped with p-ZnO. The p-n junction photocatalyst p-ZnO/TiO2 was characterized by UV-vis diffuse reflection spectrum, scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and the fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr2O72 and photocatalytic oxidation of methyl orange (MO). The results showed that the photocatalytic activity of the p-n junction p-ZnO/TiO2 is much higher than that of TiO2 on the photocatalytic reduction of Cr2O72. However, the photocatalytic activity of the photocatalyst is much lower than that of TiO2 on the photocatalytic oxidation of methyl orange. Namely, the p-n junction photocatalyst p-ZnO/TiO2 has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. When the amounts of doped p-ZnO are 0.0 and 2.0 wt.%, illumination for 20 min, the photoreduction efficiencies are 15.7 and 42.8%, and the photooxidation efficiencies are 68.1 and 26.1%, respectively. Effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p-n junction principle. (C) 2008 Elsevier B. V. All rights reserved.