Provided is a method for evaluating a positive electrode active material. The method evaluates the performance of a positive electrode active material comprising a lithium transition metal oxide that contains a manganese-containing transition metal oxide. In this method, the lithium penetration rate into a transition metal site in the lithium transition metal oxide is evaluated based on the intensity ratio P between a first-neighbor Mn—O peak intensity A and a second-neighbor Mn-M peak intensity B in a radial distribution function obtained from EXAFS at the K absorption edge of manganese (Mn). Moreover, the ratio of excess lithium present in the positive electrode active material may also be evaluated based on the excess amount of added lithium Q contained in excess of the stoichiometric ratio of the lithium transition metal oxide and the intensity ratio P.