The polypyrrole (PPy) and polypyrrole-Au (PPy-Au) nanocomposite films have been sonoelectrochemically synthesized on St-12 steel electrodes using the galvanostatic technique. Experimental design according to the Taguchi method has been applied to optimize the factors on the synthesis of PPy-Au nanocomposite coating. Three factors were used to design an orthogonal array L9: Synthesis time (t), Current density (I), and Concentration of HAuCl4 (C). The synthesized Au nanoparticles during polymerization were characterized by Ultraviolet–visible (UV-visible) spectroscopy. Characterization of the surfaces was done by scanning electron microscope (SEM), energy dispersive X-ray spectrum (EDX), and atomic force microscope (AFM). The scanning electron microscopy (SEM) image of PPy shows a smooth surface while PPy-Au nanocomposite film has a compact morphology. Moreover, energy dispersive X-ray spectrum (EDX) is evidence for the incorporation of Au nanoparticles. The corrosion protection of coatings was investigated by open circuit potential (OCP) time trends, potentiodynamic polarization technique, and electrochemical impedance spectroscopy (EIS) in a NaCl 3.5% solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41087.