Spinel LiMn2O4 were prepared by adipic acid-assisted sol-gel method at 800 degrees C, and the cathode materials with different particle sizes were obtained through ball milling. The effects of different particle sizes on electrochemical performance of LiMn2O4 sample were investigated by X-ray diffraction (XRD), galvanostatic charge-discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. XRD data exhibits that all samples exhibit the same pure spinel phase; EIS and CV indicate that LiMn2O4 samples with smaller particle size have higher charge transfer resistance and oxidation potential than that of other samples corresponding to the extraction of Li+ ions, respectively; galvanostatic charge-discharge test shows that the particle size has significant effects on the electrochemical performance of spinel LiMn2O4 cathode materials.