A novel composite photocatalyst g-C3N4/MoO3 was prepared with a simple mixing-calcination method by tuning the amount of g-C3N4 in the dispersion. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflection spectroscopy (DRS). The g-C3N4/MoO3 composites showed high efficiency for the degradation of methylene blue (MB) dye under visible light. The optimum photocatalytic activity of g-C3N4/MoO3 at a g-C3N4 weight content of 7% under visible light irradiation was almost 4.2 and 1.9 times as high as that of the pure MoO3 and g-C3N4, respectively. The enhancement of visible light photocatalytic activity in g-C3N4/MoO3 should be assigned to the effective separation and transfer of photogenerated charges originating from the well-matched overlapping band-structures. The photocatalytic degradation of MB over g-C3N4/MoO3 composites followed the pseudo-first-order reaction model. (c) 2013 Elsevier B.V. All rights reserved.