Vanadia supported on zeolites were prepared and characterized by N-2 physisorption, FTIR. XRPD, and NH3-TPD methods. The influence of the Si/Al ratio on the total surface acidity of the catalysts as well as the optimum V2O5 content were studied and compared with the catalytic activity in the selective catalytic reduction (SCR) of NO with ammonia. The SCR activity was found to correlate directly with the total acidity of the catalysts and showed high poisoning resistivity after doping with potassium oxide (100 mu mol/g). The poisoning resistance was due to unique combination of high surface area, acidity and micropore structure of the support. Apparently the support hosted the potassium oxide on the acid sites, thereby protecting the active vanadium species from poisoning. Zeolite based catalysts might therefore prove useful for SCR of NO in alkali-containing flue gases from, e.g. biomass fired power plants. (C) 2010 Elsevier B.V. All rights reserved.