MCM-41 and Aerosil-200 functionalized with different quantity of SO3-groups were used as catalysts for the heterogeneous synthesis of camphene from alpha-pinene. The characterization of the catalysts was made by thermodesorption of NH3 and physisorption of nitrogen. Three types of acid sites were found on the functionalized MCM-41, whereas on Aerosil-200 mainly strong acid sites were found. The conversion of a-pinene increased with the quantity of medium strength acid sites. The highest conversion was 100% with yield to camphene of 39.3% for catalyst with the higher content of SO3-. The highest yield to camphene was 42.2% with a conversion of 95% and was reached for moderate acid treatment of catalyst. The Aerosil-200 based catalyst did not show conversion of alpha-pinene. Other terpenes as limonene, terpinolene and delta-terpinene were obtained as by products. (c) 2007 Elsevier B.V. All rights reserved.