We applied 5 wt% V2O5/TiO2 catalysts supported on two types of TiO2 having distinctive pore structure, mesopore (DT-51) and micropore (microporous TiO2; micro) to selective catalytic reduction of NOx with NH3 (NH3 SCR) to investigate the effect of pore structure of TiO2 on sulfur poisoning. During the SCR reaction in the presence SO2 for 12 h, 5 wt% VT (DT-51) showed more drastic decrease in activity than 5 wt% VT (micro). Larger amount of SO2 was desorbed over the post-reaction 5 wt% VT (DT-51) sample during the temperature programmed decomposition which was consistent with the elemental analysis. Such larger amount of sulfate formation could be explained by the more active SO2 oxidation on the 5 wt% VT (DT-51) than 5 wt% VT (micro) because SO2 oxidation is the key step to generate sulfate species on the catalysts. It could be ascribed to the difference in the tendency of oxidation reaction affected by the vanadium species, since it was known that more V-O-V bonds existed on the surface of 5 wt% VT (DT-51) having bulk-like VOx species whereas V=O bonds were prevalent on 5 wt% VT (micro) having more dispersed VOx. In situ FT-IR results also provided the evidence about the formation of ammonium bisulfate through strong interaction between NH3 and SO3 on 5 wt% VT (DT-51), although 5 wt% VT (micro) did not. It can be summarized that the different vanadium species determined by the pore structure of TiO2 have a significant effect on the sulfur poisoning during SCR reaction.