MReO(4) (M = Ag, Na, K, NH(4), Ca, Zn) were converted with Me(3)SiCl in MeCN to Re(2)O(7) and ReClO(3) and then with SnMe(4) to the title MeReO(3) purified by double sublimation and leaching with org. solvents and then used as catalyst in epoxidation of cyclohexene and 1,5-cyclooctadiene with H(2)O(2)-pyridine or H(2)O(2)-urea complexes in CH(2)Cl(2) or CHCl(3) for 24 h or 2 h, resp. AgReO(4) was soluble In MeCN and most convenient as the feedstock. Petroleum benzin showed low soly. of MeReO(3) and was selected for leaching the crude MeReO(3). High conversion (up to 99%) of cyclohexene in presence of pure MeReO(3) (both synthesized and com. one) was achieved. The conversions of 1,5- cyclooctadiene in presence of com. MeReO(3) synthesized one did not differ substantially (60-85% and 64-77% resp.) The traces of MeCN in pure MeReO(3) considerably inhibited the epoxidation.