Organic polymer films have been used widely as electrical insulating materials. With the development of modern technology, working conditions have become more and more severe. Therefore, electrical insulating materials are demanded to have even higher reliability. Good thermal endurance of insulating materials has become also very important in recent years. Polyether-ether-ketone (PEEK) is a new engineering thermoplastic material and has good thermal, chemical, and radiation resistance. Therefore, it is expected to be applied in various fields such as electrical insulation. However, only few reports have been published on electrical properties of PEEK.1~4) In this paper, the mechanism of electrical conduction in PEEK is studied from the results of DC conduction and thermal pulse current (TPC) measurements.