A series of LiMn0.8Fe0.19Mg0.01PO4/C composites with different carbon content are synthesized and the effect of carbon content on properties of LiMn0.8Fe0.19Mg0.01PO4 is studied. The results show that the rate capability of LiMn0.8Fe0.19Mg0.01PO4/C is highly dependent on carbon content, and the LiMn0.8Fe0.19Mg0.01PO4/C with 10.5wt.% carbon exhibits the best coverage of carbon coating and the optimal rate performance. When the carbon content is reduced to 4.1wt.%, the obtained LiMn0.8Fe0.19Mg0.01PO4/C still has an excellent rate capability and can deliver a discharge capacity of 138.5 mAh g−1 at 1C, 121.7 mAh g−1 at 5C and 109.6 mAh g−1 at 10C. This is the best rate performance reported so far for low carbon coated LiMnPO4 based materials.