A lithium ion secondary battery includes at least a positive electrode, a negative electrode, and an electrolyte. The positive electrode contains at least a first positive electrode active material and a second positive electrode active material. The first positive electrode active material is expressed with a formula (I) LiNiaCobMncO2 and the second positive electrode active material is expressed with a formula (II) LiNidCoeMnfO2, where a, b, c, d, e, and f satisfy conditions of a>d, 0.4≤a≤0.6, 0.2≤b≤0.5, 0.1≤c≤0.2, a+b+c=1.0, 0.2≤d≤0.5, 0.1≤e≤0.2, 0.4≤f≤0.6, and d+e+f=1.