The antibacterial activities of cetylpyridinium-montmorillonites (CP+-Mt) were tested on Staphylococcus aureus and Pseudomonas aeruginosa. The Mt were prepared by using the five different CP+ amounts of 0.5, 0.7, 1.0, 1.5, and 2.0 times of cation exchange capacities (CEC) of Na+-Mt. Desorption of CP+ from the surface was also determined by successive adsorption-desorption experiments. The antibacterial activity tests were conducted by using Na+-Mt and CP+-Mt through the disk diffusion (Kirby-Bauer) method against the P. aeruginosa ATCC 27853, and S. aureus ATCC 29213 strains. XRD analyses of the CP+-Mt showed that basal spacing regularly increased by increasing the amount of CP+ cations. Adsorption/desorption studies revealed that desorption occurred only in 2.0 CEC CP+-Mt by dilution with water and in 1.0 CEC CP+-Mt at a pH of 2.0. Nat(+)-Mt exhibited no antibacterial activity against both bacteria. All of the CP+-Mt samples prepared were active against S. aureus, whereas they had no antibacterial activity against P. aeruginosa. Minimum inhibitory concentration (MIC) was found to be 1 mg/plate against S. aureus, determined with 0.5 CEC CP+-Mt. Because nearly no desorption of CP+ was observed, the antibacterial activity was attributed to the CP+ bound to the Mt surface. (c) 2013 Elsevier B.V. All rights reserved.