Oxidative dehydrogenation of propane over MoO3/gamma -Al2O3 catalysts with different Mo loading was studied. The catalysts were characterized by XRD, DRS, TPR, DTP and by isopropanol decomposition reaction. The results indicated that with Mo loading increasing from 3.6 to 12.7 wt.%, propane conversion increased parallel to the acidity and to the reducibility. At a conversion higher than 20% the selectivity to propene leveled off around 25% irrespective of the molybdenum content. The catalytic properties of Mo/gamma -Al2O3 appear to be related to the coordination of Mo species of the active sites and to its Brosnted acidity.