The acidity of H-beta zeolites with SiO2/Al2O3 ratios ranging from 2D to 350 was characterized by NH3-TPD profiles and FTIR spectra of adsorbed pyridine. As SiO2/Al2O3 ratios of the H-beta zeolites increased, NH3-TPD acidic amount of the samples is decreased. The IR bands of the adsorbed pyridine on the zeolites are also decreased with the increased SiO2/Al2O3 ratios. The batch reaction of propylene and benzene was carried out in liquid phase at 423 K over H-beta zeolites. The selectivity to isopropylbenzene was high. The catalytic activity of H-beta zeolites is in direct proportion to the acidic amount of the zeolites in general. H-beta zeolite of SiO2/Al2O3 = 27, which contains the highest amount of Bronsted acid sites as indicated by FTIR spectra of adsorbed pyridine, is the most reactive catalyse in the alkylation reaction. In continuous Liquid-phase reactions, high propylene conversion and isopropylbenzene selectivity can be achieved at 413-453 K with benzene to propylene mole ratio from 4 to 8. The catalytic activity and selectivity of the H-beta zeolite do not change after 1100 h of reaction.