The Friedel-Crafts reaction of biphenyl with benzyl chloride in cyclohexane was carried out over amorphous silica-alumina, in a slurry batch reactor, under magnetic stirring. Mainly benzylbiphenyl isomers (M) but also some dibenzyl derivatives (D) were obtained and determined. Within the monobenzylated fraction, a para-selectivity of 60%, almost independent of conversion, was reached. The chemically controlled reaction kinetics was interpreted by a pseudohomogeneous model of two consecutive reactions; no catalyst deactivation had to be accounted for. The best measurements were effected when the catalyst had been activated at 150 degrees C : the kinetic model, applied on the basis of an optimization procedure, was able to interpret runs carried out at different doses of catalyst and different initial concentrations of the benzylating agent. The behavior of the amorphous silica-alumina was compared with that of the HY zeolites previously used as catalysts.