Au/Al2O3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation.The activity changes of the catalyst were examined after separate treatment in CO+O2 or CO2 +O2 .Furthermore,in situ FT-IR studies were performed to investigate the species on the surface when CO or CO+O2 or CO2 +O2 was selected separately as adsorption gas.The results showed that Au/Al2O3 catalyst exhibited very high initial activity,but the catalytic activity was found to decrease gradually during CO oxidation with time on stream.And also,the activity of the catalyst declined after treatment in CO+O2 or CO2 +O2 .The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO+O2 or CO2 +O2 might be mainly responsible for the activity decrease,which was reversible. Au / Al2O3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation. The activity changes of the catalyst were examined after separate treatment in CO + O2 or CO2 + O2. , in situ FT-IR studies were performed to investigate the species on the surface when CO or CO + O2 or CO2 + O2 was selected separately as adsorption gas. The results showed that Au / Al2O3 catalyst showed very high initial activity, but the catalytic activity was found to decrease gradually during CO oxidation with time on stream. And also, the activity of the catalyst declined after treatment in CO + O2 or CO2 + O2. The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO + O2 or CO2 + O2 might be mainly responsible for the activity decrease, which was reversible.