p-n junction photocatalyst p-CaFe2O4/n-ZnO was prepared by ball milling of ZnO in H2O doped with p-type CaFe2O4. The structural and optical properties of the p-n junction photocatalyst p-CaFe2O4/n-ZnO were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflection spectrum (DRS) and fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic degradation of methylene blue (MB). The results showed that the photocatalytic activity of the p-CaFe2O4/n-ZnO was higher than that of ZnO. When the amounts of doped p-CaFe2O4 were 0.0 wt.% and 1.0 wt.%, the photocatalytic degradation efficiencieswere 50.1 and 73.4%, 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) 2009 Elsevier B. V. All rights reserved.