Isomerization of tetrahydrotricyclopentadiene (THTCPD) was conducted using three kinds of chloroaluminate ionic liquid (IL) catalysts to compare catalytic behavior of the IL catalysts. The effect of various reaction parameters and types of IL catalysts on the THTCPD isomerization has been explored to optimize the reaction process. The conversion of isomerization of THTCPD using IL catalyst strongly dependent on the molar fraction of AlCl3 regardless of the type of IL catalyst, due to an acidity variation. The characterization of the IL catalysts was also performed by means of FT-IR to elucidate the nature of acidic active species on the THTCPD isomerization. It was found that Lewis acidity can be controlled using different types of cationic species as well as by altering the molar fraction of AlCl3. Moreover, the conversion of THTCPD isomerization was strongly correlated with the Lewis acidity of IL catalyst as well. (C) 2014 Elsevier Ltd. All rights reserved.