A structural steel having excellent brittle fracture resistance, the structural steel comprising, by wt%, 0.02% to 0.12% of carbon (C), 0.01% to 0.8% of silicon (Si), 1.5% to 2.5% of manganese (Mn), 0.005% to 0.5% of aluminum (Al) , 0.02% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.0015% to 0.015% of nitrogen (N), optionally further comprising one or more selected from the group consisting of, by weight%, 0.01% to 2.0% of nickel (Ni), 0.01% to 1.0% of copper (Cu), 0.01% to 1.0% of chromium (Cr), 0.01% to 1.0% of molybdenum (Mo), 0.005% to 0.1% of titanium (Ti), 0.005% to 0.1% of niobium (Nb), 0.005% to 0.3% of vanadium (V), 0.0005% to 0.004% of boron (B), and 0.006% or less of calcium (Ca), and the balance of Fe and other inevitable impurities, wherein an outer surface layer portion and an inner central portion are microstructurally distinguished from each other in a thickness direction, the surface layer portion comprises a tempered bainite as a matrix structure, the central portion comprises bainitic ferrite as a matrix structure, and wherein the surface layer portion further comprises fresh martensite as a second structure, and the surface layer portion comprises the tempered bainite and the fresh martensite in a fraction of 95 area% or more, and wherein the central portion comprises the bainitic ferrite in a fraction of 95 area% or more, and wherein the surface layer portion comprises an upper surface layer portion in an upper portion of the steel and a lower surface layer portion in a lower portion of the steel, and the upper surface layer portion and the lower surface layer portion each have a thickness of 3% to 10% of a thickness of the steel, and wherein an average grain size of the surface layer portion is 3 μm or less, excluding 0 μm, and wherein a high angle grain boundary fraction of the surface layer portion is 45% or more, and a nil ductility transition (NDT) temperature based on naval research lab, NRL, drop weight test is -70°C or lower and a tensile strength exceeds 780 MPa, and whereby the grain sizes are determined according to the description. wherein an outer surface layer portion and an inner central portion are microstructurally distinguished from each other in a thickness direction, the surface layer portion comprises a tempered bainite as a matrix structure, the central portion comprises bainitic ferrite as a matrix structure, and wherein the surface layer portion further comprises fresh martensite as a second structure, and the surface layer portion comprises the tempered bainite and the fresh martensite in a fraction of 95 area% or more, and wherein the central portion comprises the bainitic ferrite in a fraction of 95 area% or more, and wherein the surface layer portion comprises an upper surface layer portion in an upper portion of the steel and a lower surface layer portion in a lower portion of the steel, and the upper surface layer portion and the lower surface layer portion each have a thickness of 3% to 10% of a thickness of the steel, and wherein an average grain size of the surface layer portion is 3 μm or less, excluding 0 μm, and wherein a high angle grain boundary fraction of the surface layer portion is 45% or more, and a nil ductility transition (NDT) temperature based on naval research lab, NRL, drop weight test is -70°C or lower and a tensile strength exceeds 780 MPa, and whereby the grain sizes are determined according to the description. <EOS>