The influence of thermal stabilization of NH4-Y zeolite and modification of USY zeolites with solutions of hydrochloric acid on the cyclohexylation of naphthalene in the liquid phase was studied. Removal of the part of extra-framework aluminium from zeolite structure has a positive effect on both conversion of naphthalene and amount of dicyclohexylnaphthalenes formed. Modification of zeolites leads to an increase in conversion and selectivity of β-substitution in the naphthalene cyclohexylation.