Cyclohexylation of naphthalene was studied over four commercial unmodified HY zeolites. Approximately equal results were obtained on HY (ZF 515, ZF 520, CBV 720) zeolites. The best results were obtained with cyclohexylbromide as alkylating agent in n-nonane and in n-decane as solvents at boiling point. Conversion of naphthalene was max. 97%, 2,6-selectivity 43% and beta,beta’-selectivity 77%.