Abstract: In this article Acrylonitryle Butadiene Styrene/Polypyrrole (ABS/PPy) nanocomposites were prepared by melt mixing. PPy nanoparticles were synthesized by chemical polymerization and served as nanofiller and the effects of PPy loading level on the morphology, rheological and electrical properties of ABS-based nanocomposites were examined. The synthesized PPy nanoparticles also were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Rheological properties including: shear viscosity, shear storage modulus (G’) and shear loss modulus (G"), were measured with a parallel plate rheometer using oscillation modes and the results showed that these properties increased with the PPy content and also at low frequencies G′ becomes almost independent of the frequency as PPy loading increases, suggesting an onset of solidlike behavior in these nanocomposites. Electrical conductivity measurements using four-point probe showed that increasing amount of PPy increased the conductivity of nonconductive ABS up to 10-5 S/cm. A good dispersion of PPy nanoparticles within the ABS matrix was also observed from the morphological analysis. Keywords: conducting polymers; rheological properties; nanocomposite