Catalytic epoxidation of alpha-H-containing olefins with air over nanosized metal oxides under mild conditions has been first reported. Nanosized Co3O4 was considerably active for the epoxidation of alpha-pinene and cinnamyl chloride with air at atmospheric pressure. A substrate alpha-pinene conversion of 70.75 mol% with an epoxide selectivity of 87.68% was achieved at 363 K over Co3O4. Once Co3O4 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 Co3O4 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 CoOx-SnOx (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 CoOx-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.