Polymer electrolytes have been pursued for decades by researchers to seek polymer electrolyte system that can improve the ionic conductivity with similar counterpart liquid electrolyte. Polymer electrolytes containing modified rubber, Epoxidized Natural Rubber-50 (ENR50), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and with and without plasticizer, BDG were prepared using solvent casting technique. ENR50 polymer was incorporated with various amount of ionic salt, LiTFSI ranging 20 – 30 wt. percent respectively. Non- plasticized polymer electrolyte system contained optimal 40 wt. percent of LiTFSI was successfully demonstrated at room temperature. To further increase ionic conductivity, addition of plasticizer, diethylene glycol dibutyl ether (BDG), was incorporated into the system. The effect of varied amount ranging 10, 15, 20, 25 and 30 wt. percent concentration of plasticizer on ionic conductivity value and physical properties of the polymer electrolyte films were investigated. Fourier Transform Infrared (FTIR) Spectroscopy and Electrochemical Impedance Analyzer (EIS) measurements were performed to characterize the properties of the electrolyte films respectively. FTIR spectra showed the interaction occurred between oxygen atoms of ENR polymer chain and lithium ions in the polymer electrolyte network of the system. Non-plasticized polymer electrolyte contained 40 wt. percent of ionic salt exhibited ionic conductivity 2.4474 x10^-6 Scm^-1 whereas plasticized with 30 wt. percent of BDG revealed higher value 6.6079 x 10^-5 Scm^-1 at room temperature.