LiFe0.4Mn0.6-x Ni (x) PO4/C(x = 0, 0.05, 0.1, and 0.2) composite cathode materials for lithium ion batteries have been prepared by the co-precipitation method using oxalic acid as a precipitator. The structure and morphology of precursors and products have been investigated. Electrochemical tests demonstrate that LiFe0.4Mn0.55Ni0.05PO4 can deliver a specific capacity of 142 mAh g(-1) at 0.1 C, and retains 133 mAh g(-1) after 60 cycles. The rate performance of LiFe0.4Mn0.6PO4 is obviously improved by doping Ni. The capacity of LiFe0.4Mn0.55Ni0.05PO4 at 2 C is 110 mAh g(-1).