Provided is a lithium secondary battery of a high energy density using a cathode active material having an excellent cycle characteristic in charging/discharging at a high capacity and a small irreversible capacity. The lithium secondary battery comprising: a cathode including a material that can be doped/undoped with lithium ions as an active material; an anode including a lithium metal, a lithium alloy, or a material that can be doped/undoped with lithium ions as an active material; and a liquid or solid electrolyte, wherein lithiated nickel dioxide containing tin is used as the cathode active material, and said lithiated nickel dioxide has a peak near 2&thgr;=34.4° and does not have a peak near 2&thgr;=22.5° in the X-ray diffraction pattern by CuK&agr; rays, or the intensity ratio of the peak near 2&thgr;=22.5° to the peak near 2&thgr;=34.4° is 1.2 or less.