Multilayered ultrathin films of a conductive polymer, poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) were prepared by layer-by-layer deposition technique. These films were characterized by absorption spectroscopy, atomic force microscopy, cyclic voltammetry and potential step chronoamperometry. The PEDOT/PSS films were layered up with a bilayer thickness of 5 nm and the surface roughness of the films was improved after the ultrasonicated pretreatment of a PEDOT/PSS aqueous dispersion prior to the deposition. The ultrathin films thus obtained kept excellent diffusion constant of hole carriers, 5 X 10(-10) cm(2) s(-1), as high as that of spin-cast films of PEDOT/PSS, indicating that the conducting polymer films are fabricated with nanometer-scale precision and act as a junction layer between the electrode and electrochemically active organic materials. (C) 2004 Elsevier Ltd. All rights reserved.