Investigations on ion transport properties of Mg2+-ion conducting Nano-Composite Polymer Electrolyte (NCPE) films: [80PEO: 20Mg (CF3SO3)(2)] + micro/nano sized particles of passive/active filler materials viz. SiO2, TiO2, MgO, have been reported. NCPE films have been cast by hot-press technique. Solid Polymer Electrolyte (SPE) composition: [80PEO: 20Mg (CF3SO3)(2)], identified as one of the high conducting films in an earlier study with room temperature conductivity (sigma(rt)) 2.77 x 10(-6) S cm(-1), has been used as 1st-phase host matrix and the filler particles as IInd-phase dispersoid. The effect of dispersal of different filler materials on conductivity of NCPE films has also been investigated. NCPE films exhibiting highest room temperature conductivity, referred to as Optimum Conducting Composition (OCC), has been identified from the filler particle dependent conductivity studies. The phase identification and materials characterizations on NCPE OCC film have been performed using XRD, SEM, FTIR and DSC techniques. The ion transport property has been characterized in terms of ionic conductivity (sigma) and ionic transference number i.e. total (t(ion)) and cation (Mg2+) transference number (t(+)). These ionic parameters have been determined experimentally using different ac/dc techniques. The temperature dependent conductivity measurements have also been carried out to compute activation energy (E-a) by least square linear fitting of Arrhenius plot: 'log sigma - 1/T. (C) 2013 Elsevier B.V. All rights reserved.