The effect of sulphate on the catalytic properties of V2O5/TiO2 and WO3/TiO2 in the selective reduction of NO with NH3 has been investigated. For both catalytic systems, the presence of sulphate results in the enhancement of catalytic activity without reduction of selectivity to nitrogen. The rate of NO reduction depends on the sulphate content, which is affected by the original composition of titania, the method of catalyst preparation and the metal oxide loading.