Nanocomposites of polyurethane were prepared from inorganic nano particles, (MMT), silica, , and surface modified MMT and their properties were investigated. It was shown that the molecular weight and polydispenity of nanocomposites of polyurethane were 20000 to 28000 and 1.0 to 2.0, respectively. d-Spacing for nanocomposites of MMT were increased than that of pure MMT. Initial degradation temperature of nanocomposites were 250 to . And also, the range of weight loss for nanocomposites were decreased and the end of thermal degradation was observed at higher temperatures about . The elongation at break for filled nanocomposites were the highest among the nanocomposites used in this study. studied. It was found that the tensile strength increased with increasing the filler contents while the silica nanocomposite exhibited the lowest increase and the nanocomposite the highest.