In order to enhance the photocatalytic activity of TiO2, the recombination of photogenerated electron-hole pairs needs to be suppressed. Noble metals, e.g. Au nanoparticles, have been incorporated with TiO2 to efficiently separate charge carriers created in/on TiO2. On the other hand, dissolved oxygen (DO) in an aqueous solution was also known to scavenge the electrons, which avoid the recombination of electrons and holes. In this study, we investigated the combined system of Au nanoparticles incorporated with TiO2 and DO to gain insight into the relationship between them using a photocatalytic degradation of 1,4-dioxane. The rate constants of 1,4-dioxane photodegradation with respect to TiO2 catalysts with three different Au loadings, as well as DO levels, indicated the DO dependency is disproportional to the Au loading amount, implying that there is an overlapping function in capturing electrons between Au nanoparticles and DO. (C) 2009 Elsevier B.V. All rights reserved.