Abstract LiFe0.5Mn0.5PO4 typically exhibits two pairs of plateaus in charge/discharge curves associated with MnPO4/LiMnPO4 and FePO4/LiFePO4 phase transformation. In this work, an additional plateau was observed at about 3.7 V in the discharge curve at relative high current rates, but not in the charge process. The additional plateau is identified to Mn3 + reduction by capacity analysis, cyclic voltammograms (CV) and galvanostatic intermittent titration technique (GITT) measurement. The capacity of additional plateau increases with the increase of discharge rates. LiFe0.5Mn0.5PO4 discharge mainly proceeds at this plateau at high current rate.