Mixed silver–copper oxide AgCuO2 is able to interact with CO at room temperature (RT). Such interaction is provided by the participation of the reactive oxygen species associated with deeply oxidized states of silver Ag(1+δ)+ and copper Cu(3-δ)+. CO conversion increases by more than about 20% when O2 appears in the reaction mixture. It indicates the contribution of catalytic oxidation over AgCuO2 with participation of gas–phase oxygen. It was shown that oxidizing ability of AgCuO2 decreased during prolonged interaction as a result of accumulation of surface bicarbonates. The rate of AgCuO2 deactivation at RT is significantly increased under wet conditions. The examination of thermal stability under reducing reaction medium showed that the AgCuO2 crystal structure is not stable at temperatures higher than 75 °C. Above this temperature, sequential decomposition takes place with the formation of Ag2Cu2O3 and, then, a mixture of Ag0 and CuO. Such transformation results in the loss of oxidizing ability at RT.