To provide a positive electrode active material to realize an inexpensive lithium ion secondary battery of high capacity and high reliability with superior high temperature preservability, and superior charging and discharging cycle characteristic.

This lithium ion secondary battery includes a lithium and manganese-contained compound oxide A composed of lithium, manganese, oxygen and at least one additive element, and a lithium and nickel-contained compound oxide B composed of lithium, nickel oxygen and at least one additive element, and at least one of the additive elements in the A and the B are the same element.