Alkylation reaction of phenol with tert-butyl alcohol (TBA) catalyzed by SO3H-functionalized ionic liquids has been investigated. The influences of different ionic liquids, reaction time, reaction temperature, reactant ratio (mole ratio of phenol to that of TBA), the amount and the recycle of ionic liquid were studied. The conversion of phenol and the selectivity of 2,4-DTBP were 80.4 and 60.2%, respectively, under optimum reaction condition. At the same time, the reaction mechanism was discussed based on the distribution of products. (C) 2004 Elsevier B.V. All rights reserved.