A clay-polyurethane nanocomposite comprising a clay and a polyurethane covalently bonded to the surface of the clay wherein the polyurethane is formed by reacting a clay-containing diisocyanate compound with a polyol, the clay-containing diisocyanate compound contains a diisocyanate compound covalently bonded to surface silanol groups of the clay and 0.5.about.5% by weight of the clay based on the diisocyanate compound, and the clay is exfoliated by the polyurethane such that no wide-angle X-ray diffraction (WAXD) peak is detected between 2.degree. and 10.degree. by XRD measurement. The clay-polyurethane nanocomposite structure has clay layers are completely exfoliated. In addition, the clay-polyurethane nanocomposite can be foamed to prepare a foamed clay-polyurethane nanocomposite.