Pyridine was found to give a significant effect on generating well-defined PEDOT films in vapor-phase polymerization. This additive was utilized for not only controlling polymerization rate but also stabilizing cation radicals of both EDOT and oligomeric chains during the vapor-phase reaction. At an appropriate pyridine concentration, the highconductivity and smooth PEDOT film was synthesized as a promising thin-film coating for optoelectronic applications.