The discharge-charge characteristics and performance of a Li/FeOOH(an) solid polymer battery are investigated. The cell uses a cathode of amorphous FeOOH with aniline derivatives (FeOOH(an)) and a polyacrylonitrile-based solid polymer electrolyte. The ionic conductivity of the electrolyte sample used for electrochemical measurements is 1.6 X 10(-3) Ohm(-1) cm(-1) at room temperature. Its anodic stability is above 4.5 V. The diffusion coefficient of Li+ ions into the cathode is found to be 2.97 X 10(-11) cm(2) s(-1) by a.c. impedance spectroscopy. Variations of impedance parameters and the diffusion coefficient are investigated during the first discharge-charge. From the results of these measurements, it is concluded that the structure of FeOOH(an) is deformed by Li+ ion insertion/extraction. The electrochemical redox reaction of FeOOH(an) is investigated by cyclic voltammetry. In the potential range 2.0 to similar to 4.0 V, the first discharge-charge is irreversible. Thereafter, reversible cycling processes take place. The initial discharge capacity is similar to 130 mA h g(-1) at a current density of 0.1 mA cm(-2).