Organobentonites were prepared to improve the compatibility between bentonites and organic phase. The change of lamellar structure after organic modification was observed. Na+ -bentonites and octadecylamine were used to exchange the Na+ which is in the layers of bentonites, and the organobentonites were obtained. Both FTIR and DTA-TG proved that octadecylamine entered the layers of bentonites, and XRD showed that the lamellar distance increased from 1.4 nm to 4.3 nm. Based on the experiment, most of the properties of Na+ -bentonites such as the ethylene blue adsorbed by bentonites, cation exchange capacity and the like are better than Ca2+ -bentonites'. The bentonites modified by octadecylamine improved the hydrophobic ability and widened the lamellar distance of bentonites, which contributes to enhancing the whole properties of composites.