In the conversion of isobutylene, a study has been made of the catalytic properties of zeolite-salt systems produced by the impregnation of Na, K and Rb forms of faujasite (SiO2/Al2O3 = 4.4) with aqueous solutions of NH4Cl, (NH4)2SO4, NaHSO4, (NH4)2HPO4 and H3BO3 with subsequent activation at 250 and 400-degrees-C. Modification of NaY makes it active in the oligomerization of iso-C4H8 at 120-150-degrees-C. In the case of chloride and sulphate systems, isomerization and cracking of the oligomers formed also occur. The dependence of the carbenium ion activity of the catalysts studied on the strength of the acids forming the salts, their concentration, the nature of the zeolite cations and the activation temperature has been established. Variation of these parameters makes it possible to control the activity and selectivity of zeolite-salt systems in hydrocarbon conversions accelerated by acidic catalysts.