A series of gold catalysts supported on TiO2 were prepared by photodeposition method. The effects of preparation parameters, such as power of UV light, irradiation time, and initial gold concentration, on the characteristics of the catalysts were studied. The catalysts were characterized by inductively coupled plasma-mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, and high-resolution transmission electron microscopy. The catalytic activity of the catalyst for preferential oxidation of CO in hydrogen stream (PROX) was measured in a fixed-bed plug-flow reactor. The reactant gas containing 1.33% CO, 1.33% O-2, 65.33% H-2 and He for balance was fed into the reactor with a space velocity of 30,000 ml/gh. The lower power source lamp can deposit small gold particles on the support, which in turn was responsible for the enhanced catalytic activity. The photodeposition method facilitates to prepare gold particles as small as 1.5 nm on the support. These catalysts were very active and selective in PROX reaction. However, the small gold particles were not stable as long as the reaction temperature was >50 degrees C. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.