The present invention relates to a process for the preparation of highly purified tetracyclododecenes, which can be a raw material of cycloolefin (co)polymers possessing excellent characters concerning their optical property, high transparency, heat resistance, and oil absorbency, from an inexpensive raw material of crude DCPD in a stable, continuous, and longstanding process. In the continuous preparation of tetracyclododecenes described in the present invention, it is possible to employ crude dicyclopentadiene, that is, dicyclopentadiene having low purity, as a raw material. It is also possible to produce highly purified tetracyclododecenes by maintaining the ratios of one, two, or three compounds selected from the group comprising isoprene, piperylene, and 1-methyl-2-norbornenes shown by the general formula (4) against the sum of dicyclopentadiene and cyclopentadiene within the specified ranges, wherein all these substances are contained in the raw material that are fed into a reactor.