The V2O5/Y2O3 catalysts were prepared and characterized. The performance of the catalysts in propane oxidative dehydrogenation was examined. The active phase of the catalysts is YVO4. The effects of Y2O3 and V2O5 in the catalyst on the reaction could be explained by their acid-base character. The promoting effect of Nb2O5 on YVO4 catalyst has been also discussed. The nature of the active sites of the catalysts was studied by means of ESR, NO-TPD and O-18(2)-isotope exchange methods. The results of ESR and NO-TPD confirmed the existence of V4+ in the catalyst. O-18(2)-isotope exchange revealed that the activation of oxygen took place on the V4+ Site associated with oxygen vacancies. The activation of O-2 is beneficial for the oxidative dehydrogenation of propane.