Spinel LiMn2O4 as a cathode material for lithium rechargeable batteries is economically prepared by a novel eutectic self-mixing method without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on the preparation. Thus, those process controls are discussed and emphasized. The prepared LiMn2O4 exhibits the initial discharge capacity of 124.8mAhg−1 and the discharge capacity retention of 98.2% after 20 cycles.