Solid polymer electrolyte thin films based on poly(ethylene oxide) (PEO) complexed with NaNO3 salt with compositions between 2 and 10 ether oxygens per sodium have been prepared using the solution cast method as a possible sodium ion-conducting polymer electrolyte system. The complexation of the films has been investigated through X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) measurements. Electrical properties have been measured as a function of composition and temperature using complex impedance spectroscopy. The maximum ionic conductivity has been found to be similar to3.5 x 10(-6) S/cm at room temperature for the composition O/Na=3:1. The transference numbers of different mobile species have been determined by means of DC polarization and combined AC/DC techniques. The complex impedance data have been analysed in conductivity and permittivity formalisms to cast light on possible ion transport mechanisms. The peaks found in the electric modulus plot have been characterized in terms of the stretched exponential parameter. (C) 2004 Elsevier B.V. All rights reserved.