||The present study is devoted to the mechanical behavior of a polypropylene reinforced by clay nano-platelets. Uniaxial tensile tests have been performed to evaluate some mechanical characteristics (stress-strain curves, Young's modulus, yield stress, strength, strain at rupture) of the nanocomposite. It is shown that the Young's modulus and the yield stress significantly increase compared to the matrix, even for a very low volume fraction (less than 3%). For the elastic properties, the three phase model proposed by Ji  predicts accurately the impact of nano- platelets on the Young's modulus, provided that a suitable choice of the interphase properties is made. The offset of the yield stress of the nanocomposite is investigated by means of Pukanszky's model () which provides good results when compared with our experimental data.