gamma-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium-tungsten and vanadium-molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195-, V2W4O194-, VMo5O195- and V2Mo4O194-) from aqueous solutions. The isopolyanion solutions were characterized by. UV-Vis and V-51 NMR spectroscopy. Vanadium, vanadium-tungsten and vanadium-molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state V-51 NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/gamma-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on they-Al2O3 surface.