Abstract: Beta zeolites with the SiO₂/Al₂O₃ molar ratio of 30 and 150 were synthesized in an extremely dense aqueous system by using tetraethylammonium hydroxide (TEAOH) as template and solid silica gel as silica source. Meanwhile, another beta zeolite sample of high SiO₂/Al₂O₃ ratio (about 150) was obtained by dealuminization of the low SiO₂/Al₂O₃ ratio (30) zeolite in an oxalic acid solution at 70℃. All three zeolites samples were characterized by XRD, SEM, N₂-adsorption and pyridine adsorption IR spectrum. The effects of their addition on the performances of a hydrocarbon cracking catalyst were investigated in a microactivity test (MAT) unit at 460℃. The results indicated that the intrusion of zeolite beta into the cracking catalyst can enhance its catalytic activity and improve the product distributions. When the zeolite beta of low SiO₂/Al₂O₃ ratio was added in the cracking catalyst, the isomerization was promoted and the selectivity to ethene and propene was increased. On the other hand, the addition of high SiO₂/Al₂O₃ ratio beta zeolites or the dealuminized one was able to enhance the aromatization of olefins, to increase the C₄ olefin yield and to lower the carbon deposition during reaction.