Novel hexadentate binding 8-quinolinolato manganese(III) complexes were proposed and conveniently synthesized for the epoxidation of olefins with aqueous hydrogen peroxide in water-acetone media with ammonium acetate and acetic acid as additives. The catalytic efficiencies of the suggested catalysts were found to be obviously superior to the traditional tetradentate salen-(MnCl)-Cl-III, due to their special hexadentate binding structures that could be easily converted to the corresponding pentadentate with pendant hydroxyl groups by opening an axial Mn-O bond in the reaction media, as supported by UV-vis spectra, in situ cyclic voltammetry, and quartz crystal microbalance characterizations. (C) 2008 Elsevier Inc. All rights reserved.