Electrochemical copolymerization of diphenylamine (DPA) with m-toluidine (MT) was carried out for different molar feed ratios of DPA in 4 M H2SO4 using cyclic voltammetry. Cyclic voltammogram (CV) of the deposited copolymer film was also recorded in 4 M H2SO4. CVs recorded during polymerization of mixture of DPA and NIT clearly reveals deposition of copolymer with different proportions of DPA unit in it. The CV characteristics show dependence on the molar feed concentrations of DPA or MT. UV-Vis spectroelectrochemical studies reveal the formation of intermediates/copolymer having units of DPA and MT in the backbone structure with a new characteristic band around 580 nm. Copolymers were synthesized for different molar concentration feed ratios of DPA and the molar composition of DPA and NIT units in the copolymers were determined by UV-Vis spectroscopy. Reactivity ratios of DPA and MT were computed by using Fineman-Ross and Kelen-Tudos methods and correlated with spectroelectrochemical results. The copolymers were further characterized by FT-IR spectroscopy and thermogravimetric analysis. (C) 2004 Published by Elsevier B.V.