Abstract: With unmodified and modified Al₂O₃ as the support, a series of Mn-Ce catalysts were prepared by impregnation method and characterized by XRD, BET, NH₃-TPD, H₂-TPR and FT-IR. The catalytic performance in the NH₃-SCR of NO_x was investigated. The results show that the sulfuric acid modification to the support decreased the metal dispersion and weakened the oxidization property of the catalyst, increased the concentration of acid sites, especially, B acid sites. Besides, the optimum temperature window ranges for SCR of the modified catalyst moved to higher temperature and broadened, and increased with the increase of modified liquid concentration. The unmodified catalyst and the catalyst modified by 0.2 mol/L solution had same SCR reactivity within the temperature range of 200-250 ℃. However, the modified catalyst showed the best resistance to SO₂ and H₂O and presented 70% NO conversion at 250 ℃.