By adding a small amount of multiwall carbon nanotubes (MWNTs) to polyethylene oxide (PEO) and a salt system, a new type of nanocomposite film was constructed. At ambient temperature, the conductivity of the PEO-salt-0.5 wt % MWNTs was nearly three orders of magnitude higher than that of the PEO-salt system. The conductive property of the nanocomposite film was characterized by ac impedance and the differential scanning calorimetry technique. (C) 2004 The Electrochemical Society.