Li2Fe1−x Mn x Si04/C cathode materials were synthesized by mechanical activation-solid-state reaction. The effects of Mn-doping content, roasting temperature, soaking time and Li/Si molar ratio on the physical properties and electrochemical performance of the Li2Fe1−x Mn x Si04/C composites were investigated. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), charge–discharge tests and AC impedance measurements. SEM images suggest that the morphology of the Li2Fe1−x Mn x Si04/C composite is sensitive to the reaction temperature. Samples synthesized at different temperatures have different extent of agglomeration. Being charged–discharged at C/32 between 1.5 and 4.8V, the Li2Fe0.9Mn0.1Si04/C synthesized at the optimum conditions shows good electrochemical performances with an initial discharge capacity of 158.1mAhg−1 and a capacity retention ratio of 94.3% after 30 cycles. AC impendence investigation shows Li2Fe0.9Mn0.1SiO4/C have much lower resistance of electrode/electrolyte interface than Li2FeSiO4/C.