In this work, Au supported over ZnO prepared by photodeposition was applied to prepare nano-size Au catalysts by utilizing UV light for the preferential oxidation (PROX) of CO. The results demonstrated that Au can be dispersed homogeneously over ZnO in the size range of 1-2 nm with a narrow size distribution. It was clearly seen that the preparation parameters (i.e. irradiation time, precipitant concentration, calcination, and storage condition) had a significant effect on the catalytic activity. Among the variables studied, low concentrations of precipitant and long irradiation time were by far the most influential on the catalytic activity. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.