The reaction behavior of CO over Au/TiO2 has been investigated by a temperature-programed surface reaction (TPSR) testing. We have found that there maybe existed four reaction processes of oxidizing CO over Au/TiO2 in the O-2-poor stream containing a trace H2O at or below 80 degrees C: (i) CO adsorbed at TiO2 sites is oxidized by H2O to form Ti-COOH species below 80 degrees C, which is desorbed into CO2 and H2O at 80 degrees C; (ii) CO adsorbed at Au sites is oxidized by H2O to form CO2; (iii) CO adsorbed at Au sites is oxidized by H2O to form H-2 and CO2 according to the water-gas shift reaction, which only occurs with the desorption of Ti-COOH species at TiO2 sites into CO2 at 80 degrees C; (iv) CO adsorbed at Au sites is oxidized by molecular O-2 to form CO2. For the three processes of H2O oxidizing CO, the chemisorption result of CO and O-2 over Au/TiO2 shows that it may be the Ti-bonded hydroxyl species (Ti OH) but not the adsorbed molecular H2O at TiO2 sites to react with CO adsorbed at Au or TiO2 sites. For the process of O-2 oxidizing CO, the non-promotion of pre-adsorption of O-2 on the formation of CO2 below 80 degrees C indicates that it may be the physisorbed molecular O-2 not the chemisorbed O-2 to directly react with CO adsorbed at Au sites. This work also indicates that the process of CO oxidation in the presence of H2O over the supported Au catalyst may be simultaneously oxidized by O-2 and H2O according to the respective process. (C) 2013 Elsevier Inc. All rights reserved.