In a non-aqueous electrolyte secondary cell having a positive electrode mainly composed of a positive electrode active material, a negative electrode, and a non-aqueous electrolyte, the positive electrode active material includes a lithium-containing transition metal complex oxide represented with hexagonal structure by the general formula LiCo1-XMXO2, wherein M is at least one element selected from the group consisting of V, Cr, Fe, Mn, Ni, Al, and Ti, and a crystallite size (110) of the lithium-containing transition metal complex oxide is greater than 1000 Å. Thereby, the thermal stability of the positive electrode active material is increased, and the discharge characteristic and the charge-discharge characteristic of the cell are improved.