An innovative composite photocatalyst ZnO/bone char (ZnO/BC) was prepared using precipitation of ZnO precursor on bone char. The UV-vis absorbance spectrum showed that ZnO/BC has strong visible light absorption. The photocatalytic activity of ZnO/BC was evaluated by degradation of methylene blue (MB) under solar simulator Irradiation; and the effects of oxygen, pH, holes (h(+)) and hydroxyl radicals (center dot OH) on the photocatalytic efficiency have been studied. Results showed that the dissolved oxygen contributes to the photocatalytic reaction in MB alkaline solution. The photocatalytic process mainly depends on the pH of the solution. In alkaline solution, OH- can be oxidized by h(+) to form active center dot OH. Meanwhile, the increase of MB on bone char enhances the contact to active h(+) and center dot OH produced on the surface of ZnO, enhancing the photocatalytic efficiency and reaction rate. The photocatalysis of ZnO/BC mainly resulted from direct oxidation of MB caused by photoinduced holes.