Liquid-phase alkylation of naphthalene with cyclohexyl derivatives as alkylating agents has been studied over HM and HY zeolites. The reaction can be carried out efficiently over HY zeolites, for which high conversions and good selectivities in 2,6- and 2,7-dicyclohexyl naphthalenes (DCN) are obtained after very short reaction times. The ratio 2,6-DCN/2,7-DCN is near to 1, as in the case of the isopropylation reaction over the same catalysts. Such a result is in agreement with the values of critical diameters of 2,6- and 2,7-dicyclohexyl and diisopropyl naphthalenes, calculated by molecular mechanics. The 2,6-dicyclohexyl-naphthalene is a crystalline compound which is easily separated from the reaction mixture by crystallization, which constitutes an interesting advantage of cyclohexylation in comparison with isopropylation.