In a non-aqueous electrolyte secondary battery provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, a positive electrode active material is a mixture of lithium-manganese composite oxide and at least one of lithium-nickel composite oxide represented by a general formula LiNi.sub.aM1.sub.1-aO.sub.2 and lithium-cobalt composite oxide represented by the general formula LiCo.sub.bM2.sub.1-bO.sub.2, and said non-aqueous electrolyte solution contains at least a saturated cyclic carbonic acid ester and an unsaturated cyclic carbonic acid ester having double bond of carbon where content by amount of said unsaturated cyclic carbonic acid ester having double bond of carbon is in a range of 1.0.times.10.sup.-8 to 2.4.times.10.sup.-4 g per positive electrode capacity 1 mAh.