A non-aqueous electrolyte secondary battery is provided with a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein positive electrode active material is a mixture of lithium-manganese composite oxide having spinel structure represented by a general formula Li.sub.1+zMn.sub.2O.sub.4 (wherein a relationship 0.ltoreq.z.ltoreq.0.2 is satisfied) and lithium-transition metal composite oxide represented by the general formula LiNi.sub.1-x-yCo.sub.xMn.sub.yO.sub.2 (wherein the relationships 0.5