Mo/SnO2 catalysts to be used for catalytic oxidation of ethanol and SnO2 were characterized by FTIR using pyridine, carbon monoxide, and methanol as probe molecules. Adding Mo to SnO2 does not modify the acidity of SnO2, but it decreases the number of acid centers. It was observed that in the process of drying the Mo/SnO2, Mo-isolated tetrahedral species developed on the surface of SnO2. These species are formed by the reaction Of Mo7O242- with basic hydroxyl species and probably also with Lewis acid sites. It was possible to observe two kinds of alcooxides at least. One of them is adsorbed on the oxygen of the Mo=O molybdenil unit and the other on hydroxyl species. The former is active for ethanol oxidation and the latter promotes the formation of by-products.