A nonaqueous electrolyte secondary battery includes a positive electrode containing a positive active material, a negative electrode containing a negative active material and a nonaqueous electrolyte. Characteristically, the positive active material comprises a mixture of a lithium transition metal complex oxide A obtained by incorporating at least Zr and Mg into LiCoO.sub.2 and a lithium transition metal complex oxide B having a layered structure and containing at least Ni and Mn as the transition metal.