In recent years, the conducting polymers are used in organic coatings as a replacement of chromate based pigments. The effectiveness of polydiphenylamine (PDPA) in the vinyl coating towards the corrosion protection of steel in acidic environment has been found out. The polymer PDPA was synthesized by chemical oxidation of diphenylarnme by ammoniumpersulfate in hydrochloric acid medium. The polymer was characterized by FTIR and XRD. The corrosion protection performance of the PDPA containing 0-5% in vinyl coating on steel in 0.1N HCl has been assessed by electrochemical impedance spectroscopy. Coatings containing more than 3% PDPA are found to offer excellent corrosion protection of steel in acid media due to redox property of PDPA. (c) 2007 Wiley Periodicals, Inc.