Laccase isolated from Coriolus hirsutus was first used in the synthesis of water-soluble conducting polyaniline. The laccase-catalyzed polymerization of aniline was performed in the presence of sulfonated polystyrene (SPS) as a template. Laccase shows remarkable advantages in the synthesis of conducting polyaniline compared to the commonly used horseradish peroxidase due to its high activity and stability under acidic conditions. The characterization of the polyelectrolyte complex of polyaniline and SPS has been carried out using UV-Vis and FTIR spectroscopy. Cyclic voltammetry and dc conductivity measurements confirmed that electroactive polyaniline was synthesized by the laccase-catalyzed polymerization of aniline. (C) 2003 Elsevier Inc. All rights reserved.