Oxidative dehydrogenation of propane has been studied on Mo/gamma-Al2O3 catalysts with 13 wt.% of MoO3 and promoted with Li. The changes induced on catalysts when the support is doped with different amounts of Li (from 0.3 to 1.2 wt.%) have been studied by BET, AAS, XRD, SEM-EDAX, TPR, DRS, XPS, Raman spectroscopy and isopropanol decomposition. The characterization of the samples showed important changes in: texture, Mo supported structure, acid-base properties and reducibility. The Li replaces Bronsted acid sites and decreases the strength of the terminal Mo=O bond. The change in the strength of the terminal Mo=O bond does not correlate with the decrease in Mo species reducibility or with the decrease in propane conversion. This behavior suggests that the terminal Mo=O bond is not the active sites for ODH of propane. The selectivity to propene increases at lower conversion whereas at higher values it leveled off around 25%. (C) 2003 Elsevier B.V. All rights reserved.