The interaction of oxygen with rhenium crystallites supported on gamma-alumina over a wide temperature range, 20-800 degrees C has been studied. Hydrogen chemisorption, oxygen uptake, and HRTEM, SAED, and XRD methods were applied to monitor morphology changes created upon heat treatment in H-2 and O-2. The structure of the surface rhenium oxide species was determined by HRTEM, Raman spectroscopy, and leaching with the cold water. The results obtained allowed us to propose a detailed mechanism of the oxidation and redispersion of Re crystallites on alumina. At 20-150 degrees C dissociative chemisorption of oxygen occurs with the possible formation of a superficial Re oxide. At 200-300 degrees C the process of oxidation of Re accelerates, with instantaneous sublimation of Re2O7 and its simultaneous adsorption as the ReO4 species on gamma-alumina. Metallic Re is still observed in this temperature range. At 400-600 degrees C, the ReO4 species on the support form two kinds of a surface compound exhibiting Al-O-ReO3 and Al-(O-ReO3)(3) structures. At 800 degrees C the surface aluminium perrhenate decomposes and a part of the Re oxide sublimes as Re2O7. The redispersion of rhenium was observed after H-2 treatment of the oxidized rhenium catalyst.