Olivine composites LiFe1-xMnxPO4/C (x = 0, 0.05, 0.1) were prepared by chelation assisted mechanochemical activation method using C2H2O4 as the chelating reagent. The structures of the prepared composites were characterized by X-ray diffraction (XRD). Cyclic voltammetry, ac impedance spectroscopy, galvanostatic charge/discharge performances were studied at room temperature. The discharge capacity of LiFe0.95Mn0.05PO4 was 155.6 mAh g-1 and 102.9 mAh g-1 at 1 C and 10 C rate, respectively. The results indicated Mn2+-doping in LiFePO4 could effectively enhance the electrochemical performances of this olivine compound especially at high charge/discharge rate. In addition, charge/discharge method was also used to characterize the low temperature properties of the different samples. The results showed that the lower the operation temperature was, the poorer the performances were. Furthermore, ac impedance measurement was used to understand the factors of the poor performances at low temperature.