Polyaniline has been successfully formed by aqueous electrochemical polymerization on carbon fibers. The coatings were formed under potentiostatic conditions with toluene-4-sulphonic acid sodium salt as the electrolyte. The effect of monomer concentration, electrolyte concentration, and the applied potential on the rate of polymerization were studied. The amount of polyaniline coatings formed on carbon fibers increased with increased aniline and electrolyte concentration. increasing the applied potential also increased the weight of coatings formed on the fibers. The presence of positive y-intercept in the weight gain plots are attributed to the adsorption of the electrolyte on the fibers before electropolymerization. The effect of the electrochemical parameters on the degradation of the polymer has been analyzed using infrared spectroscopy. (C) 2000 John Wiley & Sons, Inc.