Composite films of poly(3,4-ethylenedioxythiophene) (PEDOT)-coated over functionalized multiwalled coiled and linear carbon nanotubes (CNTs) have been fabricated by a simple oxidative electropolymerization route. The nanotubular morphology of the polymer-CNT composite is responsible for the lower charge transfer impedance, lower internal resistance, and superior capacitive response in comparison to that shown by the control PEDOT film doped by trifluoromethanesulfonate ions. This facile electrochemistry exhibited by the PEDOTCNT composite film ensues in a remarkably high coloration efficiency of 367 cm2· C-1 at 550 nm, hitherto unrealized for PEDOT; thus demonstrating the huge potential the PEDOT-CNT composite film has as cathode for the entire spectrum of electrochromic devices. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.