Abstract: Process for producing ethylidenorbornene (ENB) comprising a stage of thermal cracking of DCPD to CPD carried out in an inert fluid to which it is fed a stream of DCPD comprising virgin DCPD from cracking containing up to 10% wt of tetrahydroindene (THI) and recycled DCPD containing THI coming from the subsequent stage of formation of vinylnorbornene. The contact time of DCPD with the heat transfer fluid is of few seconds and it is sufficient to achieve a conversion of said DCPD ?95%, with little formation of oligomers. THI is then separated from the heat transfer fluid substantially free from DCPD and enriched in THI to a fractionation column.