Li0.94Mg0.03MnPO4/C　composite　cathode　materials　for　lithium　ion　battery　with　different　carbon　contents　are　synthesized　by　sol-gel　method　followed　by　heat　treatment　in　the　air.　Environmental　scanning　electron　microscopy　measurements　show　that　both　firing　temperature　and　carbon　content　affect　the　morphology　of　the　end　products.　X-ray　powder　diffraction　analysis　indicates　that　the　samples　are　olivine-structured.　The　galvanostatic　charge-discharge　results　show　that　the　optimal　firing　temperature　registers　400　A　degrees　C　and　that　the　electrochemical　performances　of　Li0.94Mg0.03MnPO4/C　are　improved　by　elevating　its　carbon　amount.　The　sample　with　an　initial　conductive　carbon　content　of　20　wt.%　gives　the　best　performances;　when　tested　at　the　rate　of　0.02C,　0.1C,　and　1.0C　between　2.8　and　4.4　V,　its　initial　discharge　capacity　reaches　145.8,　103.0,　and　72.8　mAhg(-1),　respectively,　and　maintains　at　100.1,　77.6,　and　65.4　mAhg(-1),　respectively,　after　100　cycles.