A cathode active material includes a lithium composite oxide having a crystal structure which belongs to a layered structure. The lithium composite oxide has a BET specific surface area of not less than 5 m2/g and not more than 10 m2/g. The lithium composite oxide has an average particle size of not less than 3 μm and not more than 30 μm. The lithium composite oxide, an average crystallite size calculated by an X-ray diffraction method is not less than 150 Å and not more than 350 Å.