Poly (N-methyl pyrrole) and poly (N-methyl pyrrole-co-o-toluidine) coatings were successfully electro-deposited on steel substrates in the mixed electrolytes of dodecyl benzene sulphonic acid (DBSA) with oxalic acid by cyclic voltammetric method. The morphology and compositions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FUR) techniques and Energy-dispersive X-ray spectroscopy (EDX). Electrode/copolymer/electrolyte system was studied by Electrochemical Impedance Spectroscopy (EIS). The results of EDX indicate that mixed electrolyte of oxalic acid and DBSA can dope more sulphur in the copolymer than the polymer. The FESEM results show that the morphology of the polymer and its copolymer are similar but the size of cauliflower structure in copolymer is smaller. The variation of R(po) and C(c) of copolymer as a function of immersion time shows that the water uptake reaches a steady state after 19 h of immersion time. The comparison between R(p) of PMPy and copolymer indicates that the existence of o-toluidine decreases the polarisation resistance of coat. (C) 2010 Elsevier B.V. All rights reserved.