Nanocomposites LiMnxFe1-xPO4/C (x = 1, 5/6, 2/3, 1/2) are synthesized by a sol-gel route combined with freeze drying. Fe2+ substituted samples coated by high-ordered carbon have the same olivine structure of LiMnPO4/C but reduced cell volumes. Fe2+ substituting greatly influences magnetic characteristics of LiMnPO4/C and slight amounts of Fe2P impurity in Fe2+ doped samples are verified by magnetic tests. Fe2+ substituted samples exhibit much better electrochemical properties. Among them, LiMn1/2Fe1/2PO4/C displays the best rate capacity and cyclic stability. Its initial discharge capacity reaches 140.1 mAh g−1 and remains at 132.5 mAh g−1 after 100 cycles at 2C, remarkably higher than those of LiMnPO4/C. The superior electrochemical performances are mainly attributed to small charge-transfer impedance, fast Li+ diffusion, residual carbon and existence of Fe2P with excellent electronic conductivity.