A positive electrode used in the non-aqueous electrolyte secondary battery of the present invention includes a hexagonal system lithium-containing cobalt composite oxide represented by the general expression .left brkt-top.LiCo.sub.1-XM.sub.XO.sub.2 (M=Zr, Mg, Al).right brkt-bot. obtained by synthesizing a lithium compound as a lithium source with a cobalt compound as a cobalt source to which 0.01 mol % or more and 1.0 mol % or less of zirconium is added and magnesium and/or aluminum is added through coprecipitation, as the positive electrode active material, whereby the thermal stability, load performance and charging/discharging cycle performance characteristics of the non-aqueous electrolyte secondary battery are improved without lowering its capacity and charging/discharging efficiency.