Lithium manganese oxide positive active material for lithium ion secondary battery and lithium ion secondary battery including the same

Provided are a lithium manganese oxide positive active material for a lithium ion secondary battery and a lithium ion secondary battery including the same. The lithium manganese oxide positive active material includes a spinel lithium manganese oxide of three or more types of particles having different sizes mixed therein, wherein first type particles have an average diameter of 5µm or greater, second type particles have an average diameter of 1µm or less, third type particles have an average diameter of 200 nm or less, and the average diameter of the second type particles is greater than that of the third type particles.