In this study, spinel?layered mixed composite oxides based on Mn?Ni with stable structure and high capacity was synthesized and characterized for its structural and electrochemical properties. Initially the transition metal precursor was synthesized using co-precipitation method with different impeller types (cross, circle), stirring speeds and synthesis conditions to fix an optimum synthetic condition. This method was also used to control the shape of the precursor. As the stirring speed increased, the synthesized precursors showed spherical shape, smooth surface and decreased particle size. Also, when the chelating agent was added, more obvious spherical shape and increased uniformity was observed in the precursors. After the precursor was prepared, the spinel?layered mixed structure was synthesized by mixing them with lithium precursor using calcinations. As a result of the structural and morphological characterizations of the transition metal precursor used, all the primary particles gathered to form secondary spherical particles. The transition metal precursor showed MnCO3(rhodochrosite,R-3c) structure and the final product showed spinel and layered mixed structure which was confirmed by x-ray diffraction spectrum. The electrochemical properties were tested at 0.2mA/cm2 with in a voltage range of 2.0V~4.9V using a 2032cointype lithium cell. All the samples exhibited the spinel layered mixed characteristic charge?discharge curves and particularly, the sample synthesized at 800 RPM with a cross impeller gave the highest capacity maximum of 261mAh/g. However, the mixed structure (spinel+layered) seemed to have an unstable cycling property because of structural instability of the materials. So, in order to improve the stability, the voltage range was changed and Co doping experiments were conducted. After 50 cycles approximately 170mAh/g capacity was observed in a voltage range of 2.25~4.6V. With 170mAh/g capacity, Co doped sample exhibited very high stability whereas, Co undoped samples exhibited very low stability with only 90mAh/g capacity.