5–10nm thin rod shaped LiMnPO4 nanoparticles are synthesized by an improved thermal decomposition method. The synthesis parameters such as the concentration of surfactants, reaction temperature and time, as well as the presence of a solvent play a critical role in the formation of spherical, thin or thick nanorods, and needle-shaped particles of LiMnPO4. A washing procedure to efficiently eliminate the surfactants attached to the surface of LiMnPO4 nanoparticles is presented, avoiding thermal treatment at high temperatures. A nanocomposite LiMnPO4 electrode provides a discharge capacity of 165mAh/g at 1/40C and 66mAh/g at 1C with only 10wt% of total carbon additive. The characteristics of as-synthesized and low amount of carbon coated LiMnPO4 are described as well as their electrochemical properties.