Polymer electrolyte systems consisting of poly (vinyl chloride) (PVC), poly (ethylene oxide) (PEO) as host polymers, lithium perchlorate (LiClO4) as inorganic salt and ethylene carbonate (EC) as plasticizer are prepared. The ionic conductivities of polymer electrolyte systems containing various salt concentrations are investigated by using impedance spectroscopy technique at various temperatures. The maximumionic conductivity is found to be 2.39 x 10-6 S cm-1 at room temperature for polymer electrolyte system containing 20 wt%of LiClO4 salt. Thermal stability of the various polymer electrolytes are examined by thermogravimetric/differential thermogravimetric analysis. The complex formation between polymer and salt has been confirmed in the polymer electrolytes by using X-ray diffraction studies.