The performance of V2O5/TiO2-based commercial SCR catalyst for the oxidation of gaseous elemental mercury (Hg°) with respect to reaction conditions was examined to understand the mechanism of Hg° oxidation on SCR catalyst. It was observed that a much larger amount of Hg° adsorbed on the catalyst surface under oxidation condition than under SCR condition. The activity of commercial SCR catalyst for Hg° oxidation was negligible in the absence of HCl, regardless of reaction conditions. The presence of HCl in the reactant gases greatly increased the activity of SCR catalyst for the oxidation of Hg° to oxidized mercury (Hg2+) such as HgCl2 under oxidation condition. However, the effect of HCl on the oxidation of Hg° was much less under SCR condition than oxidation condition. The activity for Hg° oxidation increased with the decrease of NH3/NO ratio under SCR condition. This might be attributed to the strong adsorption of NH3 prohibiting the adsorption of HCl which was vital species promoting the oxidation of Hg° on the catalyst surface under SCR condition.