Abstract: The acid sites of zeolite Y catalysts for alkylation of aromatics with long-chain alkenes are determined with IR and TPD. It is proved that not only very strong acid sites, but also medium strong acid sites play an important role in the reaction. Long-chain alkene is adsorbed on the surface of catalysts much more strongly than benzene is adsorbed. Long-chain alkene is activated by catalysts and react with benzene. Coking of catalysts causedby alkene is the main causative factor of deactivation of catalysts. It is supported by the results of pore structure analysis and diffusion properties.