We tried to improve the cycling performance of LiMn2O4 by substituting Fe for Mn. LiFe0.25Mn1.75O4 is the optimum composition which has a relatively large discharge capacity and the largest discharge capacity at n = 30, and the smallest percentage of capacity deterioration at n = 30, especially with (C-1 - C-30) X 100/C-1 = 5.6%. The variation of discharge capacities for the LiFeyMn2-yO4 (y = 0.0, 0.1, 0.25, 0.38, and 0.5) with cycling can be well expressed by the following equation : C-n/C-o = e(-ktn) where C-n is the discharge capacity at nth cycle, C-0 the theoretical capacity, t=t(1) + t(2) + ... +t(n) (t(n) = discharging time at nth cycle), and k and n constants.