gamma-Al2O3 supported vanadyl and iron vanadyl phosphates (VOPO4 and Fe-0.23(VO)(0.77)PO4) calcined at 550 or 650 degreesC have been investigated as catalysts for the oxidative dehydrogenation (ODH) of ethane to ethylene in the temperature range 450-650 degreesC in a fixed bed reactor operating under atmospheric pressure. Catalysts have been characterised by X-ray diffraction (XRD), BET surface area measurements, X-ray photoelectron spectroscopy (XPS), NH3 temperature programmed desorption (TPD) and temperature programmed reduction (TPR). A good dispersion of the active phase has been obtained. The presence of various vanadium species (vanadyl phosphate, V4+ and V3+ ions, V5+ and V4+ oxides) have been detected on the catalysts surface with a significantly different distribution between supported vanadyl and iron vanadyl phosphate, V4+ ion being the prevailing species on VOPO4/Al2O3 (VOP/Al). The different surface species show different acidity and reducibility. Supported vanadyl phosphate catalysts are more active than iron modified samples and catalysts calcined at 650 degreesC give better catalytic performances than those calcined at 550 degreesC. Catalytic tests promote the formation of V3+, whose fraction increases with the reaction temperature. The better catalytic properties of supported vanadyl phosphate have been attributed to the presence of surface V4+ ions.