Disclosed is a cathode active material (and secondary battery comprising the same) comprising a combination of a lithium manganese composite oxide having a spinel structure represented by the following Formula 1 with a lithium nickel composite oxide represented by the following Formula 2, the cathode active material having a broad potential region at 3.0 to 4.8V upon initial charge: LixMyMn2−yO4−zAz  (1) wherein 0.9≦x≦1.2, 0