In this study, an experiment and a reaction characteristic study were conducted to enhance the reaction activity of V2O5/WO3/TiO2 at 300 °C or less by adding selenium to the support, in a selective catalytic reduction method using ammonia as a reducing agent to remove nitrogen oxides. Se-TiO2 and TiO2 were synthesized using the sol-gel method, and used as a support when preparing V2O5/WO3/TiO2 and V2O5/WO3/Se-TiO2 catalysts. The reaction activity of our catalyst was compared with that of a commercial catalyst. The denitration efficiency of the catalyst using TiO2 prepared by the sol-gel method was lower than that of the catalyst prepared using commercial TiO2, but was improved by the addition of selenium. Thus, the effect of selenium addition on the catalyst structure was analyzed using BET, XRD, Raman, H2-TPR, and FT-IR measurements and the effect of the increase in specific surface area by selenium addition and the formation of monomer and complex vanadium species on reaction characteristics were confirmed.