A single phase of Li2CuO2 was successfully prepared by solid state reaction. The crystal structure was refined by Rietveld method using a synchrotron radiation source. Electronic structures of x =0 and 1 in Li2−x CuO2 were determined using the first principle calculation. We will discuss electrochemical properties of Li2CuO2 and changes in electronic structure of Li2−x CuO2, using both the information obtained from the calculation and that obtained experimentally. These results confirmed that Li-extraction of Li2CuO2 resulted in the oxidation of Cu2+ or O2−. The cuprate-based cathode materials have the potential showing high energy density. The calculation of electronic state will play a major role in designing the materials for Li-batteries.