The application of different techniques (diffuse reflectance-UV-vis, V-51 NMR, FT-IR of adsorbed pyridine and TPR-H-2) in the characterization of vanadia supported on mesoporous Al2O3 catalysts shows that the nature of the vanadium species depends on the V-loading. At V-content lower than 15 wt.% of V-atoms (30% of the theoretical monolayer), vanadium is mainly in a tetrahedral environment. Higher V-contents in the catalyst leads to the formation of octahedral V5+ species and V2O5-like species. Both XRD and textural results indicate that the mesoporous structure of the support is mostly maintained after the vanadium incorporation, and therefore high surface areas were obtained on the final catalysts. Al2O3-suppported vanadia catalysts are active and selective in the oxidative dehydrogenation of ethane, although the catalytic behavior depends on the V-loading. High rates of formation of ethylene per unit mass of catalyst per unit time have also been observed as a consequence of the high dispersion of V-atoms on the surface of the support. (C) 2004 Elsevier B.V. All rights reserved.