Reverse microemulsions, consisting of n-hexanol, Triton X-100, Cyclohexane and aqueous salt solutions, were used to synthesize BiOI, TiO2 and BiOI/TiO2 hybrid nanoparticles at room temperature. The particles had been characterized by X-ray powder diffraction, FT-IR spectra, TG-DSC analysis, nitrogen sorption, electron microscopy, and UV-vis diffuse reflectance spectroscopy. The photocatalytic properties of those particles were evaluated by degradation of methyl orange under visible light irradiation. The BiOI/TiO2 composites showed about 5 times higher photocatalytic performances than BiOI when the mole ratio of BiOI to TiO2 was 75%. The remarkable enhancement in the visible light photocatalytic activities of the BiOI/TiO2 heterostructures could be first attributed to the effective electron-hole separations at the interfaces of the two semiconductors, which facilitated the transfer of the photoinduced carriers. Meanwhile, the heterojunction formed between BiOI and TiO2 would further retard the recombination of photoinduced carriers. In addition, high degree of crystallization, bimodal porous structure, relative large specific surface area, and appropriate energy band gap have great contribution to the enhancement of photocatalytic performance. (C) 2011 Elsevier B. V. All rights reserved.