The acid and catalytic properties of type Y zeolites (with the molar ratio SiO2/Al2O3 = 5.1 and 6.0) were studied in the dimerization of alpha-methylstyrene. It was found that acid OH groups were present on the surface of the Y-6.0 samples of not only zeolites Y but also zeolites of other types, for example, mordenite or ZSM. A higher stability of Y-6.0 zeolites than Y-5.1 to ion-exchange and high-temperature treatment was observed. Specific features of the catalytic activity and selectivity these zeolites were revealed. The effects of concentration and strength of acid sites on the composition of dimerization products are discussed.