In a nonaqueous electrolyte secondary battery 10 containing a positive electrode 11 having a positive electrode active material capable of intercalating and deintercalating lithium ion; a negative electrode 12 having a negative electrode active material capable of intercalating and deintercalating lithium ion; and a nonaqueous electrolyte, the positive electrode active material contains both lithium cobalt oxide A in which 3 to 5 mol % of magnesium are homogeneously added and lithium cobalt oxide B in which 0.1 to 1 mol % of magnesium is homogeneously added which are mixed in a mixing ratio of lithium cobalt oxide A: lithium cobalt oxide B=2:8 to 8:2. By constituting a nonaqueous electrolyte secondary battery having the above constitution, a nonaqueous electrolyte secondary battery in which the thermal stability and the higher temperature cycle property are remarkably improved without lowering the battery capacity and the load performance.