The Fe-doping LiMnPO4 (LiMn1−x Fe x PO4, x ≤ 0.5) nanomaterials are solvothermally synthesized in a mixed solvent of water and polyethylene glycol (PEG). The particle morphology can be controlled simply by adjusting the pH values of precursor suspensions. Electrochemical test shows that LiMn0.9Fe0.1PO4 nanoplates with a thickness of 20–30 nm could deliver the largest discharge capacity, which is attributed to the fast Li+ diffusion in the diffusion path of [010] crystallographic axis along the short radial direction of the nanoplates. It is demonstrated that Fe doping could significantly increase the initial reversible capacity, cycle performance and rate capability. The first discharge capacities of Fe-doped LiMnPO4 are all above 150 mAh g−1 at the discharge rate of 0.05 C. Especially, LiMn0.5Fe0.5PO4 delivers 100% capacity retention with the reversible capacity of 147 mAh g−1 at the discharge rate of 1 C, and losses only about 23.4% capacity with the discharge rate varying from 0.1 C to 5 C. The variation of energy density predicts that LiMn0.5Fe0.5PO4 shows the potential application for high-power devices.