The catalytic activity and stability of Au/TiO2 have been examined under ambient conditions. The best performance was obtained for a catalyst calcined at 473 K and left at room temperature for a few days. The activity for CO oxidation was greatly influenced by moisture in the reactant gas and a maximum was observed at around 200 ppm. We have also succeeded in regenerating the catalysts exposed to various environments, such as rest room, using irradiation with light. The above results show that the Au/TiO2 catalysts are very useful for indoor air quality control at room temperature without using thermal energy for regeneration.