A ruthenium-catalyzed asymmetric epoxidation of various olefins using tert-butyl hydroperoxide (TBHP) as the oxidant is reported. By applying ruthenium(pyridinebisoxazoline)-(pyridinedicarboxylate) complexes 1 [Ru(pybox)(pydic), 1] as catalysts, aromatic and aliphatic olefins yielded the corresponding epoxides at room temperature in good to excellent yields and enantioselectivities up to 65% ee. Slow addition of the stoichiometric oxidant significantly improved the yield and the chemoselectivity of the reaction.