This paper presents the results of catalytic endo- to exo-isomerization of tetrahydrodicyclopentadiene. Several zeolites were tested and influences of calcinations temperatures, Si/Al ratio and cations of the zeolites on the reaction were investigated. The results showed that HY zeolites were more active than other zeolites and Y zeolites with other cations, because of its large pore size and relative strong acidity. In all HY zeolites with different Si/Al, H-USY is best. On one hand, H-USY has more moderate acids than others. On the other hand, the high thermal stability of H-USY makes it suitable choice for recycling catalysts. In all the zeolites tested, H-USY calcined at 450 degrees C was favorable. Regeneration of H-USY showed no decrease of exo-yield while had better exo-selectivity. (c) 2005 Elsevier B.V. All rights reserved.