The efect of CO2 on catalytic activity for CO oxidation on Cu-Ce-O fluorite-type complex oxides has been investigated. CO2 played an inhibiting role in CO oxidation on the cat-alyst simlar to what happened on CeO2. As CO2 was introduced into the feed, the coliversion of CO to CO2 on the catalyst was reduced a little. At room temperature,the catalyst could easily adsorb CO2 in large amounts from the air to fbrm carbonate on its surtace.as well as from the yields at low reaction temperature As a restit,the catalyst could be poisoned by CO2 tentatively.The catalytic activity could be recovered to its imitial value on being heated at 300 ℃ or highertemperature.Cu-Ce-O catalyst showed high activity with CO conversion over 98% after being pretreated to desorb CO2 previously.