The title reaction has been investigated over Beta zeolites of different Si/Al ratio. Surface acidity has been assessed by adsorption microcalorimetry and FTIR, 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 initially accompanied by remarkable oligomerisation/cracking of the reactant alcohol and limited cracking of the solvent. The formation of the small-sized products of the side reactions is initially favoured over the cumbersome alkylation products, due to the slow diffusion rate of the latter. Transalkylation between polyisopropylnaphthalenes and naphthalene sets in, leading to increasing conversion of naphthalene with time-on-stream. For the strongly dealuminated sample naphthalene conversion reaches a maximum and then decreases; the decreasing trend seems associated to insoluble coke formation and the confinement of transalkylation at the pore mouth.