Molybdo(vanado)phosphoric heteropoly acids of Keggin structure supported on oxide supports (SiO2, TiO2, Al2O3) were used as catalysts for ethane to acetic acid oxidation in the range of reaction temperature from 250 to 400° C. Vanadium atoms introduced into Keggin structure enhanced oxidative activity of catalytic system, while vanadyl groups exchanged into cationic position diminished ethane conversion. Nature of support (acidic or base centres on the surface) influenced both ethane conversion and distribution of products. Ethane oxidation over silica-and titania-supported HPMoVx was due to the presence of regular or defected Keggin structure while low catalytic performance on alumina-supported samples was attributed to mixed Mo-V-P oxides formed as a result of HPMoVx decomposition. Presence of water vapours in the reaction mixture was indispensable both for catalysts surface modification and for acetic acid desorption. © 2005 Elsevier B.V. All rights reserved.