Described is a process for producing 1,2-epoxy-5,9-cyclododecadiene, which comprises bringing 1,5,9-cyclododecatriene into contact with hydrogen peroxide in the presence of a carboxylic acid having an acid dissociation constant K at 25° C. of 5.0×10−6≦K≦1.0×10−4. The present invention makes it possible to provide an industrially desirable process which permits the production of 1,2-epoxy-5,9-cyclododecadiene with good selectivity and facilitates control of reaction including shortening of the reaction time.