To provide a steel wire for a cord used as a reinforcing material for a tire particularly a high-carbon ultrafine steel wire having excellent ductility and high strength, and a hot rolled wire rod as a raw material therefor.

In the high-carbon ultrafine steel wire with high strength and high ductility: the difference between the tensile strength after a lapse of one week after wire drawing and the tensile strength directly after wire drawing is 50 to <350 MPa; wire diameter is ≤0.4 mm; and the tensile strength after a lapse of one week after wire drawing satisfies inequality (tensile strength) (MPa)≥3450-1500×log(do), where (do) is wire diameter (mm).