Copper chromite catalyst has a potential for use in automobile exhaust emission control. Here an experimental study has been carried out to examine the effects of sulfur dioxide and water vapor on carbon monoxide oxidation over supported copper chromite catalyst. The degree of deactivation of the catalyst under exposure to sulfur dioxide was rather severe, especially at the carbonyl site on the catalytic surface. The decrease in catalytic activity by poisoning tended to accelerate at low temperature and at high concentration of sulfur dioxide. It was only at very low concentration of sulfur dioxide that the catalyst maintained its activity to some extent. For the catalyst that maintained more than 20 % of its intrinsic activity, its activity was fully recovered by heating at 600∼800 ℃. Once completely poisoned, however, the catalyst could not be regenerated by heating or washing. The catalytic activity also tended to decrease in the presence of the water vapor if the reaction temperature was below 250 ℃. At higher temperatures above ℃ the effect of water vapor was found negligible. The catalyst deactivated by water vapor at low temperature recovered its original activity simply by heating. This implies that deactivation by water vapor is most likely due to the adsorption of water vapor.