Ethylene-vinyl acetate (EVA) copolymers/ clay nanocomposites, prepared by using nonreactive organophilic clay and reactive organophilic clay, were characterized by X-ray diffraction and by high-resolution transmission electron microscopy. The influence of gamma irradiation on the structure and properties of the pure EVA and EVA/clay nanocomposites was systematically investigated. In the presence of gamma radiation, the clay can effectively restrain the increase of the storage modulus of EVA/clay nanocomposites, which was supported by dynamical mechanical analysis. Gamma irradiation had almost no effect on the thermal properties of EVA/clay nanocomposites by using nonreactive organophilic clay, but it obviously improved the thermal stability of EVA/clay nanocomposites by using reactive organophilic clay. (c) 2005 Wiley Periodicals, Inc.