Nanoparticles of polypyrrole (PPy) in 40/60 wt % natural rubber (NR)-polystyrene (PS) blends were synthesized by emulsion polymerization using ferric sulfate [Fe(2) (SO(4))(3)], sodium dodecyl sulfate (SDS), and n-amyl alcohol as the oxidant, surfactant, and cosurfactant, respectively. The NR/PS/PPy blends were characterized by Fourier transform infrared spectroscopy (FTIR), elemental analysis, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). FESEM micrographs showed that NR/PS/PPy blends were homogeneous, and PPy nano-particles were well distributed throughout the binary matrix of NR/PS. The size of PPy particles in the blends was in the range of 26-80 nm. The electrical conductivities of the pellets prepared from NR/PS/PPy blends increased as the composition of PPy nanoparticles was increased, which were in the range of 8.9 x 10 (8) - 2.89 x 10(-4) S/cm. Thermal stability of the blends increased as the content of PPy was increased, as shown by TGA thermograms. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2115-2121, 2012