The highly effective ZnO/g-C3N4 photocatalysts with different ZnO amount were prepared by an economic and environmentally friendly method. The photocatalysts were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, and Brunauer-Emmett-Teller surface area. The results showed that photocatalytic activity of the photocatalyst was much higher than that of pure g-C3N4 via photodegradation of Rhodamine B under visible light irradiation. The kinetic constant of RhB degradation over ZnO(15 wt.%)/g-C3N4 was 3.1 times that of pure g-C3N4. Effect of ZnO content on the photocatalytic activity of ZnO/g-C3N4 was studied in detail. The active species in RhB degradation were examined by adding a series of scavengers. The study on photocatalytic mechanism revealed that the electrons injected directly from the conduction band of g-C3N4 to that of ZnO, resulting in the production of center dot O-2(-) and center dot OH radicals in the conduction band of ZnO. Simultaneously, the rich holes in the valence band of g-C3N4 oxidized Rhodamine B directly to promote the photocatalytic degradation reaction. This work may provide some insight into solving the unsatisfactory catalytic activity and low efficiency converting solar radiation for practical applications of g-C3N4. (C) 2012 Elsevier B.V. All rights reserved.