Oxidative dehydrogenation of propane has been studied on V2Os/TiO 2 and MoO3/TiO2 catalysts, consisting of 1 and 5 monolayers of the deposited oxides, promoted with Li, K and Rb cations. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and by isopropanol decomposition, a probe for acid-base properties. For both types of catalysts, irrespective of the vanadium or molybdenum content, the total activity in oxidative dehydrogenation of propane decreased for the promoted catalysts in the sequence: non-promoted >~ Li > K > Rb-promoted catalyst. The propene yields and selectivities at equal conversion increased in the same order. The same sequence was also observed for the increase in the rate of acetone formation and the decrease in the rate of propene formation in the isopropanol decomposition on the promoted catalysts. It is proposed that the alkaline promoters decrease the acidity and increase the basicity of the catalysts, and hence facilitate desorption of propene from the catalyst surface, preventing it from further oxidation to carbon oxides. The XPS data suggest that the alkaline promoters increase the dispersion of the vanadia or molybdena phase in lhe high vanadium or molybdenum content catalysts.