The deactivation and regeneration phenomenon during room temperature CO oxidation was studied over a Au/gamma-Al2O3 catalyst, which was as active as the most active supported Au catalysts reported in the literature. The initial rapid loss of activity could be prevented if either hydrogen or water vapor was present in the reaction mixture. Otherwise, it could be recovered by exposure of the deactivated catalyst to either hydrogen or water vapor at room temperature. Thermal treatment above 100 C in a dry atmosphere also deactivated the catalyst. These results suggested that hydroxyl group, most likely associated with a Au(I) cation, is associated with the active site and support the proposal that the active site is an ensemble of Au+-OH- together with AU(0) atoms. The CO oxidation reaction was proposed to proceed via the insertion of CO into the Au+-OH- bond to form a hydroxycarbonyl, which is oxidized to a bicarbonate. Decarboxylation of the bicarbonate completes the reaction cycle.