Plasticized nanocomposite polymer electrolytes (PNCPEs) based on poly(vinyl alcohol) (PVA)–MI (M=Na, K, Ag) dispersed with nanofillers Al2O3 and plasticized with poly(ethylene glycol) (PEG) have been prepared by solution cast technique. The structural properties of the samples have been characterized using various experimental techniques such as XRD, DSC, FTIR and B-G spectroscopy. The ionic conductivity and dielectric constant of the samples have been estimated using a LCZ meter in a wide temperature range, i.e. from 30 to 170 °C. It has been observed that the presence of water molecules in polymer electrolytes significantly affects the mobility of ionic species. The temperature dependent ionic conductivity shows the Arrhenius type behavior separated in three distinct regions. The ionic transference number for all PNCPE samples is found to be ≈1, which strongly suggests their ionic nature.