The electrical property and defect structure of 12 m/o CeO2-ZrO2, which has been known for good mechanical and thermal properties, were studied in order to investigate the possibility of its use as a solid electrolyte for electrochemical device, like electrolyser, sensor and fuel cell. The electrical conductivity of 12 m/o CeO2-ZrO2 was greatly enhanced and electrolytic domain boundary (EDB) was also extended to low P-O2 with yttria doping, which were readily comparable with those of commercial electrolyte, YSZ, CSZ. Unlike normal stabilized zirconia, saturation point of electrical conductivity appeared at higher doping concentration (12-15 m/o yttria) and the activation energy was not also changed seriously with doping till 15 m/o yttria doping.