Provided is a lithium-cobalt-manganese oxide having the formula Li[Co_xLi_(1/3-x/3)Mn_(2/3-2x/3)]O₂(0.05X0.9) which provide a stable structure and a superior discharge capacity, and the method of synthesizing of the same. The method of synthesizing the oxides according to the present invention comprises: preparing an aqueous solution of lithium salt, cobalt salt, and manganese salt; forming a gel by burning the aqueous solution; making oxide powder by burning the gel; forming a fine oxide powder having a layered structure by the twice of treatments. The lithium-cobalt-manganese oxide synthesized according to the present invention has a stable and superior electrochemical characteristic. The oxide is synthesized by simple and low cost heat treatment process.