Abstract: Bentonite ismodified with cetyltrimethylammonium bromide (CTMAB) to imp rove interlayer space and the hydrophobic of Bentonite. The modified bentonite was characterized by XRD, IR and DSC techniques. The results show that the basal spacing values of the modified Bentonite is increased from 1. 2443 nm to 1. 9968nm; The symmetrical and dissymmetrical stretching peaks of cymene,methylene and hypocymene are p resent at 2912 cm- 1 and 2840 cm- 1 , and the C2H symmetrical bending peak comes out at 1498 cm- 1 in the FTIR spectra of the modified Bentonite; The endothermic peaks in the region 300 - 600 ℃ are attributed to the stepwise removal of interlayer CTMAB of the modified Bentonite. So the cetyltrimethylammonium bromide has been intercalated into the layers of Bentonite, and its character is steady at normal temperature.