There is provided a novel method for producing a bifunctional epoxy monomer which comprises reacting diolefin with a hydrogen peroxide aqueous solution, in the presence of molybdenum or tungsten oxide as a catalyst to selectively epoxidize a double bound at a specific position. The bifunctional epoxy monomers provided by the present invention are substances widely used in various industrial fields such as chemical industry, as materials for resist materials (particularly solder resist materials), and intermediates of agrochemicals and medicines, and various polymers such as plasticizers, adhesives and coating resins.