Composites of polymer electrolyte (PEO:NH4I) with graphene have been prepared and characterized. Dispersal of graphene is found to introduce partial electronic conductivity in the ion conducting polymer electrolyte. The conductivity vs. composition of graphene plots exhibit two peaks. Conformational and structural changes have been investigated by Raman spectroscopy, differential scanning calorimetry (DSC) and positron annihilation lifetime spectroscopy (PALS). The peaks in the conductivity have been explained on the basis of changes in crystallinity of the host polymer and establishment of percolation paths. (C) 2012 Elsevier B.V. All rights reserved.