An organic phosphorus source, a complex of dodecylamine and H3PO4, was used to prepare carbon coated LiMPO4 (M=Mn, Fe or Co) particles with a solid phase reaction. The obtained LiMnxFe1-xPO4-C particles were only about 50nm, resulting from the restriction of the in-situ carbon coating layer formed by the decomposition of dodecylamine-H3PO4 complex. When used as the cathode materials of Li-ion batteries, LiMn0.7Fe0.3PO4 particles displayed a high discharge capacity of 158mAh/g and good rate performance. Using these kinds of organic phosphorus salt, no other carbon source was required to be added in preparing carbon coated LiMPO4 (M=Mn, Fe or Co) particles. This method was extended to other kind of organic amine including ethylenediamine, diaminopropane, butylamine and tetradecylamine.