A series of Pt/rAl2O3, Re/gamma-Al2O3, and Pt-Re/gamma-Al2O3 catalysts have been studied by transmission electron microscopy and energy dispersive X-ray spectroscopy. It has been shown that rhenium was not alloyed with platinum, but widely dispersed on the surface of alumina. Two types of platinum were found : (i) three-dimensional metallic particles, and (ii) small particles consisting of a few platinum atoms. Some aggregation of the platinum particles occurred during use of the catalysts in the reforming of octane. It is suggested that the interaction of rhenium with the alumina support and therefore the modification to the platinum play an essential role in promoting the enhanced stability and selectivity of these catalysts to cycloalkanes and aromatics in reforming reactions.