Polyaniline–polypyrrole composite coatings were formed on carbon fibers by potentiostatic electrochemical polymerization. Electropolymerization was done by varying the applied potential and molar feed ratio of monomers. The dual nature of the composite coatings was deduced from the current–time (I–t) curves traced during polymerization. I–t curves were also used to predict the mechanism of the formation of composite coatings. UV–vis absorption spectroscopy was used to study the electronic structure of the composite coatings.