The oxidative dehydro enation of propane was studied over VMgO catalysts in a wide range of V contents (5-45 wt%). The highest propene yields were observed for samples with low-to-medium V content. Electrical conductivity measurements demonstrated the presence of anionic vacancies, which participated to the redox catalytic cycle. The reoxidation step was shown to be rate Limiting. Microcalorimetry measurements and DRIFT spectroscopy showed that an acid/base balance was equally required. Thus, the highest propene yields corresponded to adjusted redox potential combined with a strong Lewis acidity and a mild basicity. These observations, completed by the structural properties of the VMgO solids, led to the description of the active sites for the ODHP reaction.