A series of vanadium based catalysts (VxMn(4-x)Mo3Ce3/Ti) with different vanadium (x wt.%) and manganese ((4-x) wt.%) contents have been prepared by the wet impregnation method and investigated for selective catalytic reduction (SCR) of NOx by NH3 in the presence of 8 vol.% H2O and 500 ppmV SO2. The physicochemical characteristics of the catalysts were thoroughly characterized. The SCR of NOx by NH3 (NH3-SCR) activity, especially the low-temperature activity, significantly increased with increasing V2O5 content in the catalyst until the V2O5 content reached 1.5 wt.%, which corresponds well with the redox properties of the catalyst. All of the metal oxides were well dispersed and strongly interacted with each other on the catalyst surface. V mainly exists in the V5+ state in the catalysts. The strong synergistic effect between the vanadium and cerium species led to formation of more Ce3+ species, and that between the vanadium and manganese species contributed to formation of more manganese species with low valences. All of the catalysts exhibited strong acidity, while the redox properties determined the NH3-SCR activity, especially the low-temperature activity. H2O and SO2 had severe inhibiting effects on the activity of V1.5Mn2.5Mo3Ce3/Ti. However, good H2O and SO2 resistance and high NOx conversion by V1.5Mn2.5Mo3Ce3/Ti could be achieved in the presence of SO2 and almost no decline was observed in a long-term test at 275°C for 168 hr in the presence of SO2 and H2O, which can be attributed to the sulfate species formed on the catalyst surface.