Layered O2-lithium manganese oxide (O2-Li0.7[Li1/6Mn5/6]O2) was prepared by ion-exchange of P2-sodium manganese oxide (P2-Na0.7[Li1/6Mn5/6]O2). P2-Na0.7[Li1/6Mn5/6]O2 precursor was first synthesized by using a sol-gel method, and then O2- Li0.7[Li1/6Mn5/6]O2 was produced by an ion exchange of Li for Na in the P2-Na0.7[Li1/6Mn5/6]O2 precursor. Structural and electrochemical analyses suggested that good quality O2-Li0.7[Li1/6Mn5/6]O2 was prepared from P2-Na0.7[Li1/6Mn5/6]O2 synthesized at 800 oC for 10 h using glycolic acid as a chelating agent. During the cycle, the discharge profile of the synthesized samples showed two plateaus at around 4 and 3 V, respectively, with a steep slope between the two plateaus. The discharge curve at 3 V escalated with an increase in the cycle number, presenting a phase transition from a layered to a spinel like structure. The sample prepared at 800 oC for 10 h using glycolic acid delivered a discharge capacity of 187 mAh/g with small capacity fading.