The Au-TiO2 and Ag/Au-TiO2 nanoparticles have been prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane and water/Triton X-100/cyclohexane. The obtained photocatalysts were subsequently characterized by a BET method, DRS spectroscopy, X-ray photoelectron emission spectroscopy (XPS), scanning transmission electron microscopy (STEM) and X-ray powder diffraction analysis (XRD). For gold-doped titanium (IV) oxide nanoparticles the effect of reducing agent and stabilizer on gold particles size and photocatalytic activity were observed. The effect of crystalline form of TiO2 and gold nanoparticles size on photocatalytic activity of Au-TiO2 and Ag/Au-TiO2 in visible light were also investigated. The photocatalytic activity of noble metals modified-TiO2 powders under visible light irradiation was estimated by measuring the decomposition rate of phenol in an aqueous solution. The best photocatalytic activity revealed samples with large gold particles (similar to 90 nm) deposited on small titania nanoparticles. It was also found that the bimetallic samples (Ag/Au-TiO2) showed a higher photodegradation rate in visible region than monometallic photocatalysts. (C) 2010 Elsevier B.V. All rights reserved.