Isopropylation of naphthalene was carried out over various zeolites such as USY, H-beta, H-mordenite, and ZSM-5. A non-microporous catalyst, fluorinated resin, was also included for comparison. The influence of the zeolite structure and reaction parameters was studied for this reaction. A high beta,beta- and 2,6-selectivity was observed with twelve-member ring zeolite. Under the reaction conditions, 1 atm, 200 degrees C, with a feed of naphthalene:isopropanol:cyclohexane = 1:2:10 (mole ratio) and space velocity WHSV = 3.02 h(-1), 92% naphthalene conversion and a beta,beta-selectivity of 90% was obtained with USY catalyst. In any case, USY zeolite exhibits the highest activity and stability of all the catalysts. Although the selectivity to 2,6-diisopropylnaphthalene on USY is somewhat less than those on H-beta and H-mordenite, its high activity and stability can overcome this weak point. For USY, the reaction temperature of 200 degrees C gives the highest naphthalene conversion.