To utilize visible light more effectively in photocatalytic reactions, carbon-supported CuO-BiVO4 (CuO-BVO@C) composite photocatalyst was prepared by hydrothermal process and impregnation technique. The photocatalytic activities of as-prepared catalysts were evaluated by degradation of methylene blue (MB) in aqueous solution under visible light irradiation, it was found that CuO-BVO@C exhibits the highest photocatalytic degradation activity with the pseudo-first-order rate constant K, five times higher than pure BiVO4, which could be assigned to the synergistic effect of CuO-BiVO4 heterojunction and carbon spheres. The characterization of photocatalysts by a series of joint techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-vis diffuse reflectance spectra, PL spectra and electrochemistry technology, discloses that carbon spheres play two crucial roles in enhancing of photocatalytic activity. One is to act as a dispersing support to suppress the grain growth, the other is to act as a photosensitizer to transfer the electrons to CuO-BiVO4 heterojunction, which narrows the band gap of BiVO4, hinders the electron-hole pair's recombination. extends the absorption range of visible light, and improves the photocatalytic performance of catalyst. The photocatalytic degradation pathways mainly involve the formation and reaction of (OH)-O-center dot radicals. Based on the experimental results of electron spin-resonance spectroscopy, a reasonable mechanism was also proposed to elucidate the role of carbon spheres in the CuO-BVO@C composite as a photocatalyst for degradation of organic pollutants. (C) 2011 Elsevier B.V. All rights reserved.