A positive electrode active material for a secondary battery contains a lithium metal composite oxide having a crystal structure based on a rock salt structure belonging to the space group Fm-3m. The lithium metal composite oxide contains at least one element A1 selected from the group consisting of Fe, Ca, Cr, Na, Al, Si, Mg, Cu, Zn, Pb, Sb, and W. The content of the element A1 in the lithium metal composite oxide is 10 ppm by mass or more and 1000 ppm by mass or less with respect to the total amount of the lithium metal composite oxide. A lattice constant a, which indicates a length in an a-axis direction of a crystal lattice of the lithium metal composite oxide is 4.09 Å or more and 4.16 Å or less.