Visible light-activated sulfur-doped g-C3N4 photocatalysts were successfully synthesized using thiourea as sulfur source. The obtained photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microcopy, ultraviolet-visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and transient photocurrent response. The sulfur-doped g-C3N4 photocatalysts show beneficial effects on visible light absorption, electron-hole pair generation and separation. The sulfur species doped in the samples was identified as S2- to replace N atoms in the g-C3N4 framework. The photocatalytic activities of the sulfur-doped g-C3N4 under visible light were evaluated by hydrogen evolution from water splitting in aqueous solution containing methanol. The sulfur-doped g-C3N4 photocatalyst showed the highest photocatalytic performance with H-2 evolution rate of 12.16 mu mol h(-1), about 6 times higher than un-doped g-C3N4. It can be concluded that the sulfur species play a vital role and act as active sites in the photocatalytic reaction. This novel sulfur-doped g-C3N4 can be potentially used in energy and environmental applications. (c) 2013 Elsevier Ltd. All rights reserved.