Bentonite has been proven to be effective in enhancing the membrane behavior of clay, by which landfill liners can have better barrier performance toward the migration of contaminants. In this study, sodium bentonite amended locally available natural clay (Fukakusa clay) was investigated for its membrane behavior. The chemico-osmotic efficiency coefficient, omega, was obtained under different concentrations of KCl solution (1, 5, 10, and 50 mM) at pH ranging from 4.0 to 11.0. It was found that to continually decreased as the KCl concentration increased, which is consistent with Gouy-Chapman theory. pH values were found to have a significant effect on membrane behaviors, especially on the alkaline condition. According to the results, the membrane behavior under alkaline condition was 1.2-2.5 times higher than that under acidic conditions. The similarity of membrane behavior between 4.0 and 7.0 reflect the existence, but very slight erosion effect, of acidic solution. It was further found that bentonite amended Fukakusa clay possess excellent buffer capacity to resist pH change. The mechanisms of the membrane performance change were discussed with the assistance of X-ray Diffraction patterns (XRD), free swelling results, X-ray Fluorescence results (XRF), scanning electron microscope (SEM) and camera images. (C) 2014 Elsevier B.V. All rights reserved.