A series of LiFe1−x Mn x PO4/C materials with high Mn content (0.7≤ x ≤0.9) are synthesized by solid state reaction. The samples have mesoporous structure with an average pore size of 25nm, particle size around 200–300nm, crystalline size around 30nm and specific areas around 50m2 g−1. Their electrochemical performances are studied and the reversible capacity and rate performance decrease with the increase of Mn content. The redox potential of the Fe2+/Fe3+ and Mn2+/Mn3+ redox couple also shift accordingly. The overpotential value of the Mn2+/Mn3+ redox couple (80mV) is close to that of the Fe2+/Fe3+ couple (60mV) in all three compositions and shows a maximum (∼300mV) in the regions of voltage transition.