Poly(N-methylpyrrole) coatings have been electrodeposited on steel substrates from aqueous oxalate solutions. The formation process of the coatings was found to be different between acidic and basic mediums. In an acidic medium, the reactions were characterized by two stages: formation of the passive interphase and electropolymerization of the N-methylpyrrole. The composition of the formed interphase and poly(N-methylpyrrole) coatings were examined by infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). Our results show that the interphase formed in an acidic medium is composed of iron(II) oxalate dihydrate. The formation of poly(N-methylpyrrole) coatings on steel occurred after the passivation of steel was completed. Interaction between the poly(N-methyl pyrrole) coatings and the interphase is shown by the broadening of the -CO absorption peak.