Liquid-phase alpha-pinene isomerisation at 100degreesC in a batch reactor is studied over Beta zeolites synthesised by different methods. It is confirmed that alpha-pinene forms a carbenium ion in an acidic environment, which rearranges without capture by nucleophiles, to form mainly hydrocarbons as camphene, terpinenes, terpinolenes and heavy products. The microporous Beta samples show low activity despite the high acidity most probably because of the hindered intermediate formation. The nature of the enhanced activity of Beta mesopores samples is suggested to be a result from the high accessibility of the acidic sites. (C) 2004 Elsevier B.V. All rights reserved.