Octahedral　layered　birnessite　(OL)　was　synthesized　by　redox　method,　and　OL　supported　Ag　catalysts　(xAg/OL,　x　=　0.1wt%,　0.2wt%,　0.3wt%,　0.5wt%)　were　prepared　by　ion　exchange　method.　Then　catalysts　were　characterized　by　XRD,　SEM,　BET,　H2-TPR,　TG,　O2-TPD　and　in-situ　DRIFTS,　while　the　catalytic　activity　of　CO　was　evaluated.　Among　xAg/OL　samples,　the　0.3Ag/OL　exhibited　the　best　catalytic　activity　for　CO　oxidation　(T50　=　105o　C　and　T90　=　135o　C).　The　results　show　that　the　chemical　adsorption　of　oxygen,　the　low-temperature　reducibility　and　the　strong　interaction　between　the　Ag　species　and　OL　are　related　to　the　excellent　catalytic　activity　of　xAg/OL.　The　reaction　mechanism　was　studied　by　in-situ　DRIFTS.　First,　O2　was　adsorbed　and　activated　on　the　oxygen　vacancies　of　xAg/OL,　then　formed　oxygen　free　radical　attacked　the　adsorbed　CO　and　produced　CO2,　subsequently　CO2　desorbed　from　the　catalyst　surface.　Oxygen　vacancies　was　supplemented　by　gas　O2,　thus　circulating.　©　2020　Trans　Tech　Publications　Ltd,　Switzerland.