Infrared spectroscopy and temperature-programmed desorption have been used to investigate the acid-base properties of alkali cation exchanged X zeolites incorporated with boron. Boron led to decrease the acidity of fresh catalyst rapidly and to lower the acidity-decay during the reaction, side-chain alkylation of toluene with methanol. But boron can not affect the basicity, significantly. In conclusion, it seems reasonable that the role of boron is to help the activation of methyl group of toluene, which accelerates the side-chain alkylation of toluene selectively.