The plasticized PEO-KOH films have been investigated using the electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The conductivity of films increased by about 2 orders of magnitude from 10-5 to 10-3 S cm-1 at r.t. on addition of 0.5 wt.% of ethylene sulphite (ES). The degree of crystallinity was calculated from the XRD patterns. SEM micrographs show that the plasticized films were porous. The highest conductivity of plasticized films at r.t. was (1.3 ± 0.2) x 10-3 S cm-1 for the film with 0.5 wt.% of ES content. The number density of mobile ions was shown to increase indicating that ES has dissociated more salts into ions and thereby increasing the conductivity.