Disclosed are an electrode active material having improved energy density and a lithium secondary battery including the same. More particularly, provided is an electrode active material including a first electrode active material and a second electrode active material, each of the first electrode active material and the second electrode active material having a composition represented by Formula (1) below, a ratio of lithium to metals in the first electrode active material being 1.4 to 1.7, and a ratio of lithium to metals in the second electrode active material being 1.2 or more and less than 1.4: (1−x)LiM′O2−yAy−xLi2MnO3−y′Ay′  (1) wherein M′ is MnaMb; M is at least one selected from the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is at least one selected from the group consisting of anions such as PO4, BO3, CO3, F and NO3; 0