A study of the thermovacuum treatment of alpha -Al//2O//3 on the conversion of chemisorbed ethanol showed that the chemisorption capacity of this oxide increases with increasing dehydroxylation and the release of the reactive thermodesorption products into the gas phase is altered. These products correspond to dehydrogenation and dehydration. The structure of the sites formed in the dehydroxylation of alpha -Al//2O//3 and the intermediate surface complexes are discussed.