EPDM/organoclay nanocomposites were prepared by a melt mixing of a semicrystalline EPDM grafted with maleic anhydride and an organoclay (Cloisite 20A) in an internal mixer. XRD and TEM analysis revealed that the EPDM/clay forms a partially exfoliated nanocomposite and the silicate layers of the clay are uniformly dispersed at a nanometer scale in the rubber matrix. DSC studies indicated that the clay nanoparticles caused an increase in the nonisothermal crystallization temperature of the EPDM. Tensile and dynamic mechanical analysis showed that a small amount of the clay nanoparticles effectively enhanced the stiffness of the EPDM without adversely affecting its flexibility. The EPDM/clay nanocomposites were used to produce foams by using a batch process in an autoclave, with supercritical carbon dioxide as a foaming agent. The exfoliated nanocomposite produced a microcellular foam with average cell size as small as 6.23 μm and cell density as high as 2.4×1010 cell/cm3.