Provided is a positive electrode active material which includes an inner region that is a region from the center of the positive electrode active material particle to R/2, and an outer region that is a region from R/2 to the surface of the positive electrode active material particle, wherein R is a distance from the center of the positive electrode active material particle to the surface thereof. The positive electrode active material further includes 25% to 80% of crystallites C with respect to a total number of crystallites in the outer region. The crystallites C have a high crystallite long-axis orientation degree of 0.5 to 1 and a low crystallite c-axis orientation degree less than 0.5. Thus, the positive electrode active material has high capacity characteristics and a small amount of gas generated.