Provided is a lithium ion positive electrode active material for a secondary battery that can realize a high operating voltage and a high capacity while suppressing capacity drop with cycles by using a low-cost material. A positive electrode active material for a secondary battery, which is a lithium manganese composite oxide represented by the following general formula (I)
Lia(MxMn2-x-yYy)(O4-wZw) (I)
wherein in the formula (I), 0.5≦x≦1.2, 0<y≦0.3, 0≦a≦1.2, and 0<w≦1; M contains at least Fe and may further contain at least one selected from the group consisting of Ni, Cr and Cu other than Fe; Y is at least one selected from the group consisting of Li, Be, B, Na, Mg, Al, K, Ca, Ti and Si; and Z is at least one of F and Cl.