Hydration of alpha-pinene and esterification of alpha-terpineol have been investigated in the presence of various acidic ionic liquids. It was found that the cations of ionic liquids determined catalytic performance of acidic ionic liquids, and the anions had obvious effect on the selectivity of desired products. It was also found that ionic liquid 1-methyl-3-(3-sulfopropyl)-imidazolium dihydrogen phosphate ([HSO3-pmim]H2PO4) exhibited outstanding catalytic properties in both reactions. Furthermore, the effective product isolation combined with the recyclable catalyst is expected to contribute to the development of clean and environmentally friendly strategy for the synthesis of alpha-terpineol and alpha-terpinyl acetate. (c) 2007 Elsevier B.V. All rights reserved.