A non-aqueous electrolyte secondary battery is provided that has a high discharge capacity and in which the structure is stable even when lithium is extracted to a high potential so that good cycle performance can be obtained. A non-aqueous electrolyte secondary battery has a negative electrode, a non-aqueous electrolyte, and a positive electrode having a positive electrode active material comprising sodium oxide, characterized in that: the sodium oxide contains lithium; and the molar amount of the lithium is less than the molar amount of the sodium.