TiO2/reduced graphene oxide composite (T-rGO) was synthesized and its performance was evaluated with photocatalytic hydrogen evolution. It was found that the hydrogen evolution rate of T-rGO increased significantly after injecting small amount of air into the vacuum pumped and UV irradiated sealed reaction cell. The IR, XPS, Raman and ESR spectra analysis indicated that the O-2(center dot-), which generated from the reaction of photoinduced electrons and the injected O-2 can moderately and controllably increase the oxygen groups on graphene planar of T-rGO at ambient condition. The amount of oxygen groups on graphene planar of T-rGO will affect the p-doping concentration of graphene, thus affect the p-n junction and the performance of T-rGO for photocatalytic hydrogen evolution. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.