Polypropylene/graphite nanocomposite foams with nano scale cellular structures were prepared after sorption of CO2 at temperature 160 oC in batch foaming process. PP/graphite nanocomposites foams showed lower density and more uniform fine-scale cells in compare with PP foam. This uniform nano-scale structure was accompanied with improving mechanical properties. Nanocomposite foams with average cell size smaller than 200nm showed higher ultimate stress and tensile modulus due to the effect of CO2-induced crystallization. CO2 sorption thickens the crystalline lamellae and consequently increases Tm from 165 to 180oC for both pure PP and PP/graphite nanocomposites. Beside the properties improvement due to CO2-induced crystallization, ultimate specific tensile strength and modulus in nanocomposites foams advanced more than 10 and 40% over PP foam, respectively. It was attributed to the nucleation effect of graphite which caused to form finer crystal particles.