The object of the present invention is to provide an industrial and economical process for preparing (E2)-cis-6,7-epoxy-2-nonenal of the following formula (3): The present invention provides a process for preparing (E2)-cis-6,7-epoxy-2-nonenal (3), comprising at least steps of: subjecting (Z3,Z6)-3,6-nonadien-1-ol of the following formula (1) to oxidation: to form (E2,Z6)-2,6-nonadienal of the following formula (2); and epoxidizing the resulting (E2,Z6)-2,6-nonadienal to form the aforesaid (E2)-cis-6,7-epoxy-2-nonenal (3).