Abstract: The TPD of surface oxygen of Fe₂O₃, Sb₂O₄ and other five mixed oxides with atom ratio Sb/Fe from 1/9 to 9/1 have been investigated. A small amount of oxygen is desorbed from Fe₂O₃ at 200-450℃ while for Sb₂O₄the desorption peak of oxygen appears after 700℃ and in the case of mixed oxides both α and β oxygen are found to be during TPD after 400℃. It is found that the activation energy of desorption of a oxygen increases with the increase of Sb content and that α oxygen is more reactive than β oxygen for the oxidation of propylene. It is shown also that NH₃ adsorption sites are of different strength depending on the content of α and β oxygen in Fe-Sb oxide. It is concluded that suitable bonding strength of surface oxygen in Fe-Sb oxides should be the main cause of high activity and selectivity in the ammoxidation of propylene.