Montmorillonite-rich clay was fractionated from bentonite mined from Kampo area in Korea, and it was treated with many cationic organo-surfactant. The chemical and physical characteristics of them are investigated, and epoxy nanocomposites were also studied. To calculate the exchanged content of organo-surfactant, thermogravimetric was carried out and interlayer distance was measured by wide-angle X-ray diffractometer. The interlayer distance for MMT-III, HDA-M, ODA-M, CTMA-M, and ODTMA-M were 1.21, 1.53, 1.57, 2.04, and 2.07 nm. All organobentonites were delaminated in the epoxy matrix forming the epoxy/organobentonite nanocomposites with various contents. Tensile strength and Young's modulus were modified by loading the organobentonite. (C) 2004 Elsevier B.V. All rights reserved.