The title reaction has been studied on various HY-based catalysts. Surface acidity has been evaluated by adsorption microcalorimetry and FTIR analysis, using pyridine as probe molecule. Catalytic tests were carried out at 623 K and 40 bar in liquid phase, with decalin as solvent, in flow reactor. Isopropylation is accompanied by oligomerisation/cracking of the reactant alcohol, cracking of the solvent, isomerization of the products of the main reaction. Pore filling by coke is fast for non-dealuminated HY, where naphthalene conversion remains high due to the occurrence of transalkylation between polyisopropylnaphthalenes trapped in the pores and naphthalene; this does not occur on dealuminated HY, owing to the low density of the acid sites and the presence of a secondary mesoporous system which allows easy diffusion of the reaction products in the zeolite pores.