LiAlO2 composited LiMnPO4/C cathode material has been synthesized by in-situ growth hydrothermal method. The coexistence of minor LiAlO2 in LiMnPO4 plays an important role in electrochemical properties. The composite is characterized by XRD, SEM, HRTEM, Raman microprobe spectroscopy and their electrochemical properties are also studied. It shows that the LiAlO2 is composed of pure α-LiAlO2 phase with flaky-shaped nanoplates. LiAlO2 nanoplates porous structure is inherited from anodic aluminum oxide (AAO) structure and serves as substrates to grow LiMnPO4 nanocrystals, which provide a high surface area with a porous structure. The structure of LiMnPO4 is not affected by LiAlO2 nanoplates compositing. Among the investigated samples, the one with 6wt.% LiAlO2 exhibits a higher specific discharge capacity of 142.8mAh/g at 0.05C rate with a high capacity retention of 94.8% after 50 cycles. Electrochemical impedance spectroscopy (EIS) results show that the lithium diffusion constant (DLi + ) for 6wt.% content LiAlO2-LiMnPO4/C electrode is 2.07×10−14 cm2/s which is higher than the values for other contents LiAlO2-LiMnPO4/C electrode. The LiAlO2 is effective in suppressing the increase of the interfacial resistance between the electrode/electrolyte interface during charge-discharge cycling.