Electropolymerization of 3-chloroaniline on a platinum electrode in an acid medium was carried out under different reaction conditions of temperature, current density and hydrochloric acid and monomer concentrations with duration time. The initial rate of the electropolymerization reaction was small, and the orders were 0.99, 0.96 and 1.2 with respect to current density and acid and monomer concentrations, respectively. The apparent activation energy was 41.6 kJ/mol. The rate law was R-P = k(2)(Current density)(0-99) [HCl] (0.96)[Monomer](1.2). The obtained polymer films were characterized by H-1-NMR, elemental analysis, IR spectroscopy, and cyclic voltammetry. The mechanism of the electropolymerization reaction is also discussed. Thermogravimetric analysis was used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. X-ray and scanning electron microscopic analysis are used to investigate the surface morphology. (C) 2004 Wiley Periodicals, Inc.