The present invention relates to a positive electrode active material including a lithium transition metal oxide which contains 60 mol% or more of nickel based on a total number of moles of transition metals excluding lithium and is in a form of a secondary particle in which primary particles are aggregated, wherein the lithium transition metal oxide satisfies Equation 1 in the specification, a method of preparing the positive electrode active material, and a positive electrode and a lithium secondary battery which include the positive electrode active material.