The activation energy of thin films polymers made of pure polyethylene oxide (PEO) and PEO doped with sodium iodide  (0.1 % wt.) was investigated. The observed physical constants of the casted thin films such as the activation energy (Ea) were determined. The films were prepared by casting method using electricity. The present study investigated the variation of the activation energy of thin films of pure (PEO) and PEO doped with sodium iodide (0.1 % wt.) with the variation in frequency in the range of (200-800) kHz and in the temperature range between (30 -55) ^oC. The results proved that there is a significant change in the values of the activation energy (Ea) for both studied thin films with the variation in frequency. It was found that the values of the (Ea) of the prepared thin films are decreased by doping PEO with sodium iodide (0.1 % wt.). The values of (Ea) for both studied thin films decrease with the increase in frequency.