The alkylation of benzene with dodecene over HY zeolite is studied in a stirred batch reactor. A special feature of the effect of the benzene to dodecene ratio on the reaction conversion is found. Even a low water content (0.04%) in the reactants greatly decreases the reaction conversion. The catalyst is deactivated quickly because of the coke formation in the zeolite. A special method of regenerating the deactivated catalyst has been developed. It consists of extracting the deactivated catalyst with one of reactants, benzene. The regeneration temperature has a great effect on the activity of the regenerated catalyst. It is also found that at a similar reaction conversion, there is the same product distribution for the deactivated catalyst and the regenerated catalyst. The isomer distribution in the product can be explained by the product shape-selective mechanism.