The colloidal stability of montmorillonite (MMT,) dispersions in aqueous NaCl solution and in alcohol-water mixture has been studied in this work. The study was performed through the measurements of particle size, zeta potential, surface tension and swelling capacity. The experimental results have shown that the stability of colloidal MMT dispersion is distinct in the two cases, although the zeta potential has the same change trend. This observation might be attributed to the different behavior of surface tension in aqueous NaCl solution with alcohol water mixture. The former would increase the surface tension of the media that deteriorate the wettability and swelling capacity of MMT, while the latter would decrease the surface tension. It is demonstrated that the surface tension of the media would affect strongly the colloidal stability of aqueous MMT dispersions, which is of great importance in many industrial processes as well as in soil chemistry and environmental science. (C) 2017 Published by Elsevier B.V.