The compound [Fe(H2O)](0.20)(VO)(0.80)PO4 was studied for NH3-adsorption properties and catalytic activity towards NO reduction by NH3, Adsorption properties were studied by means of temperature programmed desorption (TPD) and FT-IR techniques. FT-IR investigation gave evidence of the presence of strong Lewis acid sites and less strong Bronsted acid sites, The NH3 uptake increased in the presence of water vapour due to an increase in the concentration of surface acid sites and due to some NH3 intercalation. Catalytic activity measurements, performed under diluted feed conditions at T = 250-450 degreesC and a contact time of 9 x 10(-3) s, gave NO conversion up to 60%, with small N2O production. Addition of water vapour to the feed caused not only a slight decrease in NO and NH3 conversion but also a marked decrease in N2O formation, thus enhancing the reaction selectivity. This behaviour was ascribed to an inhibiting effect of water on NH3 oxidation.