Vapor-phase isomerization of endo-tetrahydrodicyclopentadiene (endo-THDCPD) to exo-THDCPD over zeolite catalysts (HY, H-USY, H beta, HZSM-5 and HMOR) was studied as a green synthesis route for exo-THDCPD. The HY and H-USY catalysts showed catalytic activity while the H beta, HZSM-5 and HMOR catalysts did not. Higher yield of exo-THDCPD was obtained over the H-USY catalyst than that over the HY catalyst, attributing to the presence of strong acid sites and mesopores in the H-USY catalyst. The yield of exo-THDCPD obtained via vapor-phase isomerization was better than that reported via liquid-phase isomerization. In addition to the properties of the catalyst itself, the vapor-phase isomerization process of endo-THDCPD was also affected by the reaction temperature, the concentration of endo-THDCPD, the contact time and the time on stream. Under the optimized conditions, high purity (>98 wt%) exo-THDCPD was directly obtained without any separation processes. Although deactivation of the catalyst with the time on stream was observed, the activity could be recovered easily via regeneration in air. (C) 2011 Elsevier B.V. All rights reserved.