Provided is a method of preparing a positive electrode active material, which includes preparing a mixture by mixing a lithium compound, a transition metal precursor, and a metal oxide additive, and sintering the mixture to form a lithium transition metal oxide, wherein the sintering is performed through two-stage temperature holding sections, a temperature of a first temperature holding section is in a range of 400° C. to 650° C., and a temperature of a second temperature holding section is in a range of 700° C. to 900° C. A positive electrode including a positive electrode active material prepared according to the method, and a lithium secondary battery including the positive electrode is also provided.