WO3/g-C3N4 two-dimensional (2D) composite photocatalysts were prepared through a simple hydrothermal method followed by a post thermal treatment. The H-2 generation activity of these photocatalysts in the visible light was evaluated. The photocatalysts were characterized by X-ray powder diffraction, Fourier transform infrared spectra, transmission electron microscopy and UV-vis diffuse reflectance spectroscopy et al. These results show that the orthorhombic-phase WO3 nanoparticles with a grain size from 5 to 80 nm were successfully anchored on g-C3N4 nanosheets surface with intimate contact. Furthermore, the charge separation mechanisms of photo-generated charge carriers of the 2D WO3/g-C3N4 photocatalysts were further studied by photoelectrochemical response and electrochemical impedance spectroscopy. The result shows that the 2D WO3/g-C3N4 photocatalyst with 10 wt% WO3 possesses the maximum photocatalytic performance for H-2 generation, as high as of 1853 mu mol h(-1) g(-1), which is about 6.5 times higher than that of bare g-C3N4, indicating the fast injection of interface interaction between 2D g-C3N4 and WO3. The increased photocatalytic performance of the composite photocatalyst can be attributed to the enhanced absorption of visible light, the higher photo-generated electrons and holes separation efficiency and low recombination rate of electrons and holes generated by photoexcitation. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.