The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, to a bimodal-type positive electrode active material that includes a first lithium composite oxide which is a small particle and a second lithium composite oxide which is a large particle, which have different average particle diameters, thereby improving an increasing deviation of an average particle diameter and degraded impedance and lifetime characteristics due to excessive calcination for any one of the small and large particles during simultaneous calcination, a positive electrode including the same, and a lithium secondary battery using the same.