Nanoparticle inorganic filler ceria, CeO2 is incorporated into polyethylene oxide (PEO)-NH4ClO4 salt complex. Ceria nanoparticles improve the thermal stability of PEO salt composites. Two crystalline phases are found in thermal studies. Interfacial interaction of ceria with PEO is confirmed by the systematic variation of Fourier transform infrared spectra. The addition of ceria enhances the conductivity of PEO complex by one order of magnitude. The highest conductivity of 3.61 x 10(-4) Scm(-1) is obtained for 25 wt.% CeO2. (C) 2007 Elsevier B.V. All rights reserved.