The present invention is directed to a positive electrode active material for non-aqueous electrolyte secondary batteries that can reduce direct-current resistance while it contains a nickel-containing lithium transition metal oxide with a high Ni content. The positive electrode active material contains lithium borate and a nickel-containing lithium transition metal oxide (Ni≥80 mol %) having a layered structure. The nickel-containing lithium transition metal oxide is composed of secondary particles formed by aggregation of primary particles. Lithium borate is attached to the surfaces of the primary particles. The proportion b of lithium borate with respect to the total molar amount of metal elements other than lithium in the nickel-containing lithium transition metal oxide is in the range of 0 mol %