The effect of oxidation-reduction treatment on the dispersion and reducibility of Re/gamma-Al2O3 catalysts (1.04 and 10.4 wt% Re) was studied by hydrogen chemisorption, transmission electron microscopy, electron diffraction, electron spin resonance and X-ray diffraction. It was found that oxidation at room temperature or at 673 K causes a significant (two-or three-fold) increase of Re dispersion in the catalysts reduced at 823 K. Two different mechanisms of redispersion of Re particles are proposed and discussed depending on the oxidation treatment applied. Reducibility of Re in the oxidised catalysts was found to he dependent on Re content and on the pretreatment procedure.