A cathode active material for a secondary battery including a lithium-manganese composite oxide having a spinel structure and represented by the following general formula (I), Li.sub.a(M.sub.xMn.sub.2-x-y-zY.sub.yA.sub.z)(O.sub.4-wZ.sub.w) (I), wherein 0.5.ltoreq.x.ltoreq.1.2, 0.ltoreq.y, 0.ltoreq.z, x+y+z<2, 0.ltoreq.a.ltoreq.1.2 and 0.ltoreq.w.ltoreq.1; M contains at least Co and may further contains at least one element selected from the group consisting of Ni, Fe, Cr and Cu; Y is at least one element selected lo from the group consisting of Li, Be, B, Na, Mg, Al, K and Ca; A is at least one of Ti and Si; and Z is at least one of F and Cl. When the cathode active material for the secondary battery is used as the cathode for the a secondary battery, a higher operating can be realized while suppressing the reliability reduction such as the capacity decrease after the cycles and the deterioration of the crystalline structure at a higher temperature.