In this work, isomerization reaction of alpha-pinene was studied over several heat-treated natural zeolite catalysts, rich in clinoptilolite, from Balykesir-Bigadic region in Turkey in a batch slurry reactor under nitrogen atmosphere. Zeolite samples were calcined at different temperatures such as 300, 450 and 600degreesC. All catalysts were tested in the isomerization reaction of alpha-pinene and were characterised by nitrogen adsorption experiments, IR, and XRD measurements. Acidity strength and the distribution of Lewis and Bronsted acid sites of the samples were determined. Selectivities to main reaction products, camphene and limonene, and reaction kinetics were investigated. Catalytic activity, that is total conversion of alpha-pinene, of heat-treated samples decreased with increasing calcination temperatures. Selectivity to limonene is dependent on alpha-pinene conversion at high conversion levels while the selectivity to camphene is not. The formation of heavy products increased with treatment temperature. It was seen that alpha-pinene consumption could be described by a first-order kinetics. (C) 2004 Elsevier B.V. All rights reserved.