In this study, NH3 treatment of CeO2 was found to significantly enhance its NH3-SCR performance. The NH3- treated CeO2 was characterized by BET, XRD, TPR and XPS. The obtained results revealed the excellent SCR activity and stability of CeO2 catalyst treated by NH3 should be originated from the dropped crystallinity, better reducibility, along with the production of more Ce3+ and surface adsorbed oxygen. Furthermore, in situ DRIFT study has been carried out and the results indicated that the Langmuir-Hinshelwood (L-H) mechanism could be applied for explaining the SCR reaction route over CeO2-N.