Thin films of poly(methyl methacrylate) (PMMA) with lithium triflate (LiCF 3 SO 3 ) were prepared by using the solution-casting method with PMMA as the host polymer. Ionic conductivity and dielectric measurements were carried out on these films. The highest conductivity for polymer electrolyte with a ratio of 65:35 was found to be 9.88×10 −5 S cm −1 , which is suitable for the production of mobile phone battery. Thermal gravimetric analysis was carried out to evaluate the thermal stability of the polymer electrolyte. The addition of salts will increase thermal stability of the polymer electrolyte.