The effect of Ce on the activity and alkali resistance of V 2 O 5 /TiO 2 catalyst for the selective catalytic reduction (SCR) of NO x by NH 3 has been investigated. It was found that the addition of Ce not only reduced the vanadium loading of V 2 O 5 /TiO 2 but also enhanced its activity and alkali resistance. The NO x conversion over 0.5%V 2 O 5 -5%CeO 2 /TiO 2 was much higher than that over 1%V 2 O 5 /TiO 2 catalyst. Based on the catalyst characterization, the redox cycle (V 4+ +Ce 4+ ↔V 5+ +Ce 3+ ) can account for the excellent NH 3 -SCR catalytic performance of 0.5%V 2 O 5 –5%CeO 2 /TiO 2 catalyst. In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) measurements revealed that the role of Ce on the V 2 O 5 –CeO 2 /TiO 2 catalyst was to contribute to the formation of NO 2 and monodentate nitrate species, both of which were reactive intermediates for the NH 3 -SCR of NO x .