Rhenium oxides supported on zeolite Y, mixed silica-alumina and pure alumina were prepared by impregnation of the supports with Re2O7 or NH4ReO4. The materials are active catalysts in the epoxidation of cyclooctene and cyclohexene with anhydrous H2O2 in EtOAc. Catalyst stabilities with regard to metal leaching are closely correlated with the alumina content of the support and almost no leaching was observed with ReO4- supported on pure alumina. Stable catalysts ReO4-Al2O3 with ReO4- contents up to 12 wt.% can be prepared. Higher contents result in extensive metal leaching and catalysis in the homogeneous phase. The catalyst ReO4(12 wt.%)-Al2O3 was re-used in three catalytic runs, without loss of activity. Selectivities for cyclooctene epoxide were around 96%, whereas cyclohexanediol was obtained as the only product in cyclohexme epoxidation. Adding pyridine to the reaction mixtures. the selectivity for cyclohexene epoxide increased from 0 to 67%, however, a significant decrease in conversion was observed.