1,2-epoxy-5,9-cyclododecadiene is produced with a high selectivity thereto by epoxidizing 1,5,9-cyclododecatriene in a continuous multi-stage oxidation apparatus having a plurality of reactors connected to each other in series in such a manner that (1) in a first reactor, 1,5,9-cyclododecatriene, hydrogen peroxide, catalyst components and optionally a mineral acid are subjected to an epoxidation reaction; (2) the resultant reaction mixture delivered from the first reactor is passed through one or more succeeding reactors to further epoxidize the non-reacted 1,5,9-cyclododecatriene with the non-reacted hydrogen peroxide; and (3) the final reaction mixture produced in a rearend reactor is delivered from the oxidation apparatus, and optionally subjected to an isolation-refining procedure wherein the target 1,2-epoxy-5,9-cyclododecadiene is refined and collected and the non-reacted 1,5,9-cyclododecatriene is recovered and recycled to the epoxidation procedure.