Abstract: A lithium secondary battery is produced by employing a charging method where a positive electrode upon charging has a maximum achieved potential of 4.3 V (vs. Li/Li+) or lower. The lithium secondary battery contains an active material including a solid solution of a lithium transition metal composite oxide having an ?-NaFeO2-type crystal structure. The solid solution has a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuK? radiation for a monoclinic Li[Li1/3Mn2/3]O2-type before charge-discharge. The lithium secondary battery is charged to reach at least a region with substantially flat fluctuation of potential appearing in a positive electrode potential region exceeding 4.3 V (vs. Li/Li+) and 4.8 V (vs. Li/Li+) or lower. A dischargeable electric quantity in a potential region of 4.3 V (vs. Li/Li+) or lower is 177 mAh/g or higher.