NOVELTY - An electrode group (1) having a positive electrode, a negative electrode, a separator and a polypropylene layer, is accommodated in a battery case (4). A voltage is applied to the positive electrode and the negative electrode, so that the electric potential of the positive electrode is 4.4 V or more with respect to the melt deposition potential of metallic lithium. The surface of the polypropylene layer which touches the positive electrode is oxidized. The battery case is sealed, and a nonaqueous electrolyte secondary battery is manufactured.    USE - Manufacture of nonaqueous electrolyte secondary battery (claimed) for house hold electronic appliance such as mobile telephone, portable personal computer and portable video camera, and electric vehicle.    ADVANTAGE - The method provides nonaqueous electrolyte secondary battery having high reliability.    DETAILED DESCRIPTION - An electrode group having a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a polypropylene layer touching the positive electrode, is accommodated in a battery case with a non-aqueous electrolyte, where the positive electrode and the negative electrode capable of occlude-discharging lithium reversibly. A voltage is applied to the positive electrode and the negative electrode, so that the electric potential of the positive electrode is 4.4 V or more with respect to the melt deposition potential of metallic lithium. The surface of the polypropylene layer which touches the positive electrode is oxidized. Gas emitted in the oxidation process is removed from interior side of the battery case. The battery case is sealed, and a nonaqueous electrolyte secondary battery is manufactured.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the nonaqueous electrolyte secondary battery.    Electrode group (1)    Battery case (4)    Insulating material (5)    Negative electrode terminal (6)    Sealed cap (7)