Disclosed are a carbon dioxide absorbent composition in which an N-alkylaminoalkanol; a polyhydroxyamine-based compound; and ethylenediamine and/or diethylenetriamine are mixed, a method for preparing the same, and a method and an apparatus for carbon dioxide absorption/separation using the same. Since the carbon dioxide absorbent according to the present disclosure has superior carbon dioxide absorption capacity and remarkably lower absorbent recycling temperature as compared to the existing absorbents such as monoethanolamine, etc., total energy consumption in the capturing process can be reduced greatly. In addition, since carbon dioxide is recovered at low recycling temperature, contamination by water or absorbent vapor may be prevented.