Two lithium manganese oxides, Li1.03Mn1.96O4, with different surface areas of 3.55 and 0.68m2/g were prepared and their electrochemical properties were studied as positive electrodes for lithium ion batteries. Cycle performance tests gave capacity losses of 9 and 18% at 25°C, and 28 and 33% at 55°C for the samples with larger and smaller surface areas, respectively. The recovery of capacity losses have been found on the addition of the conductor after cycles. The defect of the conductivity between the active materials and the conductors was found mostly responsible for the capacity loss in the smaller surface sample at 25°C. Cycle performance tests in each region of the charge states divided into five regions show that larger capacity losses are observed in rather lower potential states. Storage performances show the largest capacity loss at 10 and 20% of SOC and the less capacity losses at both 0 and 50–100% of SOC in both of the samples. However, in every region, the capacity loss is much smaller in the larger surface sample than in the smaller surface sample. The maximum Mn dissolution is observed to occur at 100% of SOC (4.5V) and the next is found around 10–20% of SOC in either sample.