A positive electrode active material is provided, including a lithium transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium transition metal oxide has 60 mol % or more nickel (Ni) with respect the total number of moles of transition metal except lithium, and is doped with at least any one doping element selected from the group consisting of B, Zr, Mg, Ti, Sr, W, and Al. The positive electrode active material has an average particle diameter (D50) of 4 μm to 10 μm after rolling at a rolling density of 3.0 g/cm3 to 3.3 g/cm3 and has the form of a single particle. A method of preparing the positive electrode active material, a positive electrode including the positive electrode active material, and a lithium secondary battery are also provided.