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LiFe 12x Mn x PO 4 /C composite materials as cathode materials in Li-ion batteries have been synthesised and their electrochemical properties have been investigated. The samples were synthesised by using high energy ball milling of commercially available precursors (Li 2 C 2 O 4 , FeC 2 O 4 .2H 2 O, MnC 2 O 4 .2H 2 O, NH 4 H 2 PO 4 ) and then heated at 600uC. The morphology and structure of the heated samples were analysed by means of SEM and X-ray diffraction. The olivine structure of the LiFe 12x Mn x PO 4 /C composite was obtained. A slight shift of the peaks to smaller 2h angles with the increasing Mn/Fe ratios is observed due to the increase in lattice parameters. The influence of different Mn/Fe ratios on electrical and electrochemical performances were studied by charge-discharge and cyclic voltammetry (CV) testing. The CV curves of the pure LiFePO 4 and LiMnPO 4 show the expected Fe 2z /Fe 3z peak around 3?5 V and Mn 2z /Mn 3z peak around 4?1 V, respectively. The addition of manganese increases the discharge voltage from 3?5 to 4?1 V.