LiMnPO4 nanoplates in a size of 30-70nm were successfully obtained via a graphene oxide (GO) assisted solvothermal synthesis method. The particle size reduction is ascribed to a preferential nucleation of LiMnPO4 on the GO sheets. The particle size is critically dependent on the added GO content, ranging from 300nm, 200nm to 50nm, when the GO content increase from 5/30, 10/30, to 20/30mg/cm-3. LiMnPO4 nanoplates were further carbon-coated at 600°C. Carbon-coated LiMnPO4 (LiMnPO4/C) with a particle size of 30-70nm displays a specific capacity of 140mA h g-1 at C/10 and 85mA h g-1 at 1C rate.