provided is a nonaqueous electrolyte secondary battery in which the structural change of a positive electrode active material is suppressed at high voltage and which can achieve high capacity and long life . the nonaqueous electrolyte secondary battery includes a positive electrode containing a positive electrode active material storing and releasing lithium ions , a negative electrode containing a negative electrode active material storing and releasing lithium ions , and a nonaqueous electrolyte . the positive electrode active material is a cobalt composite oxide which has a layered rock salt structure and which includes a lithium layer containing magnesium , magnesium is present in the lithium layer after charge is performed at a potential of 4 . 53 v or more versus lithium , and 4 . 5 mole percent to 10 mole percent of a magnesium - containing compound is present on the negative electrode with respect to magnesium in the positive electrode .