The effect of Mn on the catalytic performance of V2O5/TiO2 catalyst for the selective catalytic reduction of NOx by NH3 (NH3-SCR) has been investigated in this study. It was found that the added Mn significantly enhanced the activity of V2O5/TiO2 catalyst for NH3-SCR below 400 degrees C. The redox cycle (V4+ + Mn4+ <-> V5+ + Mn3+) over Mn-promoted V2O5/TiO2 catalyst plays a key role for the high catalytic deNO(x) performance. The redox cycle promotes the adsorption and activation of NH3 and NO, forming more reactive intermediates (NH4+, coordinated NH3, NO2, and monodentate nitrate species), thus promoting the NH3-SCR to proceed.