Poly(o-phenylenediamine-co-2-aminobenzothiazole), P(oPD-co-2ABT), has been synthesized electrochemically from an aqueous acid medium. The initial rate of electrocopolymerization reaction on platinum electrode is small, and the rate law is Rate K-E [Na2SO4](0.48) [HCl](1.09) [M](2.08). The apparent activation energy (E-a) is found to be 57.44 kJ mol(-1). The polymer films obtained have been characterized by cyclic voltammetry, X-ray diffraction, elemental analysis, TGA, scanning electron microscopy, and IR-spectroscopy. The mechanism of the electrochemical polymerization reaction has been discussed. The monomer reactivity ratios (r(1) and r(2)) were calculated using Fineman-Ross method. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 252-264, 2011