Abstract: A series of ZSM-5 zeolites were prepared by modification of thermal or inorganic acid treatment to investigate the effect of acidity on their catalytic performance. The meta-xylene (MX) transformation reaction was used as a probe reaction. The modified ZSM-5 zeolites were characterized by Py-FTIR, NH3-TPD and 27 Al NMR. It is found that a part of bronsted acid is converted to Lewis acid by thermal treatment, and a part of Al atom is removed from the framework of the zeolite by acid treatment. The catalytic test results show that at the similar conversion of MX isomerization reaction, the disproportionation reaction of MX increases as the Lewis acid proportion increases.