Manganese ion-planted MCM-41 (Mn-MCM-41) prepared by the template ion-exchange (TIE) method has been found to be active for catalytic epoxidation of aromatic olefins. The activity of Mn-MCM-41 was the greatest among those of Mn/MCM-41, Mn/SiO2, Mn/Al2O3, which were prepared by a conventional impregnation method, and Mn-ZSM-5 prepared by an ion-exchange method. The proper reaction conditions have first been determined for trans-stilbene as the substrate. The most effective oxidant was tert-butyl hydroperoxide (TBHP) at 328-348 K among H2O2, PhIO, TBHP, and O-2. The highest yield of 93% of trans-stilbene oxide was obtained by using a mixed solvent of acetonitrile and dimethylformamide of 9:1 (v/v) at 328 K. Mn-MCM-41 could be used repeatedly for the reaction without decrease in the catalytic activity. The epoxidation of trans and cis isomers of various aromatic olefins has then been studied. The oxidation of olefins having bulky substituents such as 4-tert-butylphenyl and 2-naphthyl could proceed in the mesopores of Mn-MCM-41. The epoxidation of trans isomers was easier than that of cis isomers. The olefins with cis configuration all gave the corresponding trans oxides with small amounts of trans olefins as by-products. A radical mechanism has been suggested for the oxidation on the basis of the product distributions.