In this article the effect of polypyrrole nanoparticles on the mechanical and electrical properties of acrylonitryle butadiene styrene (ABS) nanocomposite were investigated. For this porpoise polypyrrole nanoparticles were synthesized by chemical oxidative polymerization of pyrrole monomer in the present of surfactant (DBSNA). ABS/PPy nanocomposites at different polypyrrole fraction were prepared by melt mixing procedure. The synthesized PPy and nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and mechanical properties were studied using uniaxial tensile analysis. Tensile analysis showed that stiffness of of ABS/PPy nanocomposites increased by the addition of PPy concentration but elongation at break decreased. The composites exhibited noticeable improvement in thermal stability in comparison to pure ABS. Keywords: polypyrrole, thermal properties, mechanical properties