The effects of halogen ions on the activities of Al2O3, TiO2, and ZrO2 for the low-temperature SCR of NO with NH3 have been studied. The results showed that Cl- and Br- ions increased the life of the catalysts from 1 to 2 h to several tens of hours (NO removal greater than or equal to90%), F- had no clear influence on the performances of the studied metal oxides, but I- was a fatal poison to the catalysts due to the formation of 12, which would cover the active sites needed for the reaction. The doping effect of Cl- and Br- ions on the catalysts was due to the increase of both the strength of acidity and the amount of acidic sites on the surface of the catalysts, which was confirmed by the temperature-programmed desorption of NH3 from the Al2O3-based samples. On the other hand, the accumulation of nitrate salts during the reaction decreased obviously over the Cl- and Br- ions-doped samples; as a result, the average selectivity to N-2 during the reaction time increased correspondingly.