Ultrathin polymer films were fabricated by the layer-by-layer deposition of poly(acrylic acid) (PAA) and a polycation bearing ferrocene (Fc) moieties (P(CM-Fc(x))), and their electrochemical properties were investigated by cyclic voltammetry and potential step chronoamperometry. The thickness of the films was controlled with 1-nm precision. All the Fc moieties in the films were electrochemically active through electron hopping among the Fc moieties. The diffusion coefficient of the films consisting of PAA and P(CM-Fc(21)) was evaluated to be 2 x 10(-10) cm(2) s(-1). This relatively high value for the electron hopping mechanism is due to local segmental motions of the Fc moieties in the films. (c) 2005 Elsevier B.V. All rights reserved.