Provided is a positive electrode active material including a plurality of crystallites A, wherein the plurality of crystallites A has a crystallite long-axis orientation degree DoA represented by Equation 1 below is 0.5 to 1, and a crystallite c-axis orientation degree represented by a cross product value of a c-axis rotation vector Rc of a crystal lattice of a crystallite obtained by electron backscatter diffraction (EBSD) analysis and a position unit vector P′ of the crystallite is 0.5 to 1. A proportion of the plurality of crystallites A is 25% to 80% with respect to a total number of crystallites in a cross-section of a positive electrode active material. Further provided is a positive electrode and a lithium secondary battery including the positive electrode active material.