Gold loaded on TiO2 (Au/TiO2) catalysts were prepared using Au(I)-thiosulfate complex (Au(S2O3)(2)(3-)) as the gold precursor for the first time. The samples were characterized by UV-vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S2O3)(2)(3-) as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO2. The diameter of An nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal An loading from 1% to 8%. The photocatalytic activity of Au/TiO2 catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar An loading, the catalysts prepared with Au(S2O3)(2)(3-) precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO2 catalysts prepared with the methods of deposition-precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of An nanoparticles loaded on the surface of TiO2 and further affects the photocatalytic activity of the obtained catalysts. (c) 2007 Elsevier B.V. All rights reserved.