Abstract: In order to improve the activity of catalytic oxidation of NO over MnO_x/TiO₂,a certain amount of cerium nitrate was doped into the catalyst while the MnO_x/TiO₂ catalyst was prepared by impregnation on TiO₂.Ce(1)Mn(3)Ti catalyst was characterized,using XRD,BET and XPS.At the same time,the effects of H₂O and SO₂ on catalytic oxidation of NO were investigated.The deactivation mechanisms in the presence of H₂O and SO₂ were analyzed by FT-IR,SEM and BET.The results showed that Ce(1)Mn(3)Ti yielded a 58% NO conversion at 200℃,and 85% at 250℃ when the space velocity was 41 000 h^-1,O₂ and NO concentrations were 10% and 300×10^-6respectively.The activity of catalyst declined in the presence of only 4% H₂O but this negative effect could be counteracted by increasing the reaction temperature.After in the presence of 4%H₂O and 100×10^-6 SO₂ together,NO conversion was maintained at 48%.The activity of the deactivated catalyst could recover to 61% after removing H₂O and SO₂.H₂O and SO₂ make catalyst deactivation because of the active component has been sulfuric acid stalinization.