Catalysts prepared as bulk VSb0.1Ox and supported V2O5/Al2O3. V2O5-Sb2O3/Al2O3 and Sb2O3/Al2O3 (containing 0.5, 1 or 2 theoretical monolayers of V2O5 or Sb2O3) were tested in the oxidative dehydrogenation of iso-butane at 550 degrees C in i-C4H10:O-2 :He=20:10:70 gas mixture. Fresh and used catalysts were characterised by BET, XRD and XPS, Reactivity and thermochemistry of active oxygen taking part in the redox cycle with ethane and hydrogene were studied using in situ differential scanning calorimetry. Temperature-programmed desorption of O-2 in He Row was also investigated and in situ DRIFT was applied to investigate surface species of the catalysts in flows of i-C4H10, O-2 and i-C4H10/O-2 mixture. Supported VSbyOx catalysts are more active and selective than bulk one. V-only supported catalysts display a high efficiency due to the high reactivity of VOX-species. In bulk catalyst, the surface is enriched with antimony. In supported samples, the surfaces V/Sb are close to the calculated ones. In the presence of antimony, the amount of active oxygen species and their reactivity in redox transformation is improved. The rates of vanadium reduction and reoxidation are also higher. Compared to V-only catalysts, supported V-Sb-catalysts display a lower coking activity and higher on-stream stability.