The electrochemical property of Keggin type hetero polyoxomolybdate K3[PMo12O40] (KPM) as the cathode electrode material for lithium battery was examined. KPM showed charge–discharge performance in the potential region from 4.2V to 1.5V with capacity of over 200mAhg−1. From the result of the ex situ XRD measurement, it is presumed that the electrochemical reaction of KPM proceeds via the lithium (de-)intercalation. The cycle performance of KPM is largely dependent on the charge–discharge potential range. The capacity fade caused by deep discharging seems to be concerned to the 〈 to ® isomerization of KPM.