LiMn2O4 powders with different particle sizes were obtained by sieving, and the influence of particle size on the electrochemical behavior was examined. With a decrease in particle size, both the specific capacity and the coulomb efficiency become markedly increased. It is suggested that the small particles with large interface area provide more lithium ions for diffusion, leading to the high ionic current and specific capacity. The large interface area between LiMn2O4 and the liquid electrolyte also increases the opportunity for lithium ions to intercalate back into the host structure. In the cyclic voltammetry test, small LiMn2O4 particles exhibit the oxidation peaks at higher voltage during the deintercalation process. It is considered that the size of pores among LiMn2O4 particles is reduced when the particle size is decreased, and the reduced opening results in an increase in the mass-transfer resistance, therefore, more driving force is required to extract lithium ions from the cathode materials.