The effect of vanadium oxide on an iron-based catalyst supported on activated carbon (AC) in the selective catalytic reduction of NOx by NH3 (NH3-SCR) was investigated in this work A series of vanadium-modified Fe2O3/AC catalysts were prepared by a coirripregnation method. The addition of a small amount of vanadium oxide contributed to the higher dispersion of iron species On the surface of the catalyst. Among various vanadium-modified iron catalysts supported on Ac, 3% Fe-0.5% V achieved the best SCR activity and SO2 tolerance. In the presence, of H2O, SO2 had a severe deactivation effect on both vanadium- and non-vanadium-modified catalysts, yet the inhibition effectof H2O and SO2 was reversible on 3% Fe-0.5% V at relatively low space velocity. It was found that the' vanadium additive promoted the formation of sulfate species. The formed sulfate species increased the surface acidity and thus enhanced the tolerance toward SO2.