The synergetic effect over a H-ZSM-5/V2O5 hybrid catalyst on selective catalytic reduction (SCR) reaction has been studied by steady state reaction (SSA), temperature programmed reaction (TPR) and NH3-temperature programmed desorption (TPD). The improved NO conversion is observed on the layered hybrid catalyst with V2O5 as the first layer. TPR experiment suggested that V2O5 plays a role as a supplier of oxygen source through N2O formation, while H-ZSM-5 decomposes N2O into N-2 and alpha-oxygen. alpha-Oxygen may contribute to the increase in NO2 species on H-ZSM-5 and improves the apparent SCR activity. NH3-TPD by NO experiments shows the possibility of the contribution of spillover oxygen in the improvement of SCR activity. (c) 2005 Elsevier B.V. All rights reserved.