An enzymatic method for the synthesis of a water-soluble, conducting poly(o-toluidine) (POT) in the presence of sulfonated polystyrene (SPS) is presented. The enzyme horseradish peroxidase was used to polymerize o-toluidine to form a water-soluble, conducting POT/SPS complex, which exhibits moderate electrical conductivity. The synthesis is simple and the conditions are mild. The polymerization may be carried out at room temperature in pH 4.3 buffered aqueous solution with stoichiometric amount of monomer, SPS, hydrogen peroxide and catalytic amount of enzyme. The UV–Vis absorption spectra of the products display a distinct absorption peak at 740 nm at pH 4.3 that indicates the formation of the conducting, emeraldine salt form of POT. The structure and electrochemical behavior of the polymer was investigated with FT-IR and cyclic voltammetry method.