The liquid phase isomerization of a-pinene over a catalyst with 12-tungstophosphoric acid (HPW) supported on natural zeolite rich in clinoptiolite was studied in a batch slurry reactor in a nitrogen atmosphere and at constant temperature of 373 K. The catalysts prepared were characterized by nitrogen adsorption, XRD, SEM, and DSC measurements. The catalytic activity increased from 15% to 99% with the introduction of HPW at 4.25 wt% onto the natural zeolite. However, the catalytic activity decreased with the calcination of the catalyst sample. XRD studies indicated that only the HPW catalyst supported on natural zeolite without calcination was the one where the HPW crystals were formed, no significant HPW crystals were observed in the calcined sample. The main reaction products of the isomerization reaction of a-pinene were camphene and limonene with selectivities of about 40% and 3%, respectively, over the HPW catalyst supported on natural zeolite without heat treatment. One and a half order dependency on a-pinene consumption was observed and activation energy was established to be 65.4 kJ/mol. (C) 2011 Elsevier B.V. All rights reserved.