The catalytic performance of zeolite beta in the liquid-phase alkylation of benzene is compared with that of other solid catalysts. Zeolite beta is more active and more selective than zeolite Y in the alkylation with propylene and ethylene to cumene and ethylbenzene (EB). In the alkylation with propylene the overall selectivity of beta is higher than that of the traditional "solid phosphoric acid." The catalytic activity is affected by the composition and the particle size of zeolite beta samples. Decreasing the framework Al content, by direct synthesis or by partial substitution of Al for B, produces a decrease in both conversion and selectivity in cumene and EB synthesis. A hypothesis to explain this behavior is given. The catalytic activity of zeolite beta is limited by intraparticle diffusion, as evidenced by the decreased activity corresponding to the particle size increase.