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Catalytic epoxidation of a-H-containing olefins with air over nanosized metal oxides under mild conditions has been first reported. Nanosized Co 3 O 4 was considerably active for the epoxidation of a-pinene and cinnamyl chloride with air at atmospheric pressure. A substrate a-pinene conversion of 70.75 mol% with an epoxide selectivity of 87.68% was achieved at 363 K over Co 3 O 4 . Once Co 3 O 4 was further modified with metal oxides or ammonium salts through a simple procedure consisting of ultrasonic agitation, drying and calcination, thus-prepared catalysts presented lower catalytic activity and higher epoxide selectivity than cobalt oxide itself. Over Co 3 O 4 modified with surfactants, the conversion of a-pinene was somewhat reduced to 48.86-63.76 mol%, but the epoxide selectivity was increased to 92.12-94.83%. However, the composite oxide CoO x -SnO x (10:1) catalyzed 48.21 mol% of a-pinene conversion with 85.82% of epoxide selectivity. For the substrate cinnamyl chloride, the best result was 40.76 mol% of conversion and 87.17% of epoxide selectivity achieved by CoO x -ZnO (5:1). It is noteworthy that the use of TBHP in small amounts initiated the reaction efficiently, and the lack of TBHP would lead to a low conversion and selectivity.