A surface-treated electrode active material, a method of surface treating an electrode active material, an electrode, and a lithium secondary battery. The surface-treated electrode active material includes a surface metal oxide layer having higher degree of reduction of a metal than that of a bulk metal oxide layer. The method includes: forming a mixture by adding an untreated electrode active material comprising a metal oxide, and at least one of a basic material and a reducing material to a solvent; and stirring the mixture.