The catalytic properties of HY and dealuminated HY zeolites in the vapor phase t-butylation of phenol with t-butyl alcohol in the temperature range 100-200degreesC are reported. The influence of various reaction parameters such as temperature, space velocity, molar ratio of the reactants are discussed. The main products are p-t-butyl phenol (p-TBP), o-t-butyl phenol (o-TBP) and 2,4-di-t-butyl phenol (2,4-DTBP). The product distribution depends on the reaction temperature, number of acid sites and the ratio of Bronsted to Lewis acid sites, which changes with the steaming temperature. Lower molar ratio of reactants and higher space velocity facilitated mono alkylated products. (C) 2002 Elsevier Science B.V. All rights reserved.