A method of preparing a positive electrode active material for a secondary battery, is disclosed herein. In some embodiments, a method includes mixing a positive electrode active material precursor, a lithium source material, a first firing additive, a second firing additive, and a third firing additive a to form a mixture, wherein the positive electrode active material precursor contains nickel, cobalt, and manganese and has a nickel content of 60 mol % or more relative to a total molar amount of metals in the positive electrode active material precursor, and performing primary firing of the mixture to form a lithium transition metal oxide, wherein the first firing additive is a lithium-containing compound, the second firing additive is a carbonate ion-containing compound, and the third firing additive is a boron-containing compound.