A lithium ion battery with polymer electrolyte is expected as a safe and long cycle life battery. This paper reports primarily the recent development results of a solid polymer electrolyte, which is a key factor of the secondary battery system, that has been obtained during the process of the development of a polymer type lithium battery. As a successful result of the solid polymer electrolyte, a ionic conductivity of the solid polymer electrolyte, which is composed of polyacrylonitrile and LiClO4 with Al2O3 dissolved as the supporting electrolyte, has been confirmed to be 2.3x10(-4)S/cm at room temperature.