The novel cobalt-phosphate (Co-Pi) modified graphitic carbon nitride (g-C3N4) photocatalysts were synthesized by "in situ" surface photodeposition process to enhance photocatalytic H-2 and O-2 evolution performance. The resulting Co-Pi/g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The photoelectrochemical measurements of the composite materials were also performed under visible light irradiation. In the photodeposition process, the photogenerated holes in the valence band can oxidize Co2+ ions into Co3+ ions and cause the deposition of Co-Pi catalysts on the g-C3N4 surface. The photocatalytic results indicate that the Co-Pi catalysts can promote the separation of photogenerated charge carriers in g-C3N4 and enhance H-2 and O-2 evolutions. One of the synthesized samples CP-20 exhibits the highest catalytic activity. The corresponding O-2 and H-2 evolutions of the CP-20 are 6.8 and 9.6 times than the photocatalytic activities of unmodified g-C3N4. A possible mechanism on the improvement of visible light performance is proposed; and this can pave the way for the design and synthesis of new photocatalytic materials. (c) 2013 Elsevier B.V. All rights reserved.