Abstract: AIMTo investigate the mechanism of the interaction between montmorillonite and bacteria by studying the reactions of different charges of montmorillonites with bacteria. METHODSBacteriostatic test: one loop of E.coli and Staphylococcus aureus at the concentration of 1×10⁶·mL^-1 was incubated to the plate culture medium containing different concentrations of montmorillonite, and incubated 24 h to observe the growth of bacteria. Bacterial adsorptive test: different amounts of montmorillonite were added into the artificially simulated intestinal solution (containing bacteria 1×10⁷·mL^-1). After the culture, the bacterial colonies were counted. RESULTSThe results showed that montmorillonite per se showed no bacteriostatic or bactericidal effect, but after exchange with metal ion and functional groups which inhibits bacteria, then it showed these activities. Adsorption was the main way between montmorillonite and bacteria. The special way of fixing bacteria into the “carriage” of montmorillonite gel which carry this structure was its pharmacological basis of curing diarrhea. The adsorption effect was related to layer charge density of the montmorillonites. CONCLUSIONMontmorillonite showed adsorption ability of bacteria with minus related to its layer charge, but has no bacteriostatic and bactericidal effect.