Ag-Mn complex oxides were prepared by a co-precipitation method and used for carbon monoxide oxidation in a stoichiometric mixture of carbon monoxide and oxygen. They were characterized by means of XRD and H-2-TPR techniques. The XRD results show Ag and/or Ag2O are finely dispersed in Mn2O3. The crystallization of Mn and Ag species in Ag-Mn catalysts is inhibited for intimate mixing. From the TPR profiles of Ag-Mn complex oxides, alpha and beta reduction peaks are observed. Low content of Ag promotes the reduction of manganese oxides while further increasing of Ag content to more than 5% inhibits the reduction. Treatment in high temperature allows TPR peaks to recover more easily. Oxidation of CO is enhanced by increasing Ag content from 0 to 5% but is inhibited by further increasing the Ag content. This is in accordance with the temperature of reduction peaks. Ag(5%)-Mn sample exhibits high and stable activity in all catalysts, it shows no hystersis and does not decay after reaction for 36 h while retaining approximately 90% conversion of CO at 73 degreesC.