The invention discloses a high carbon steel wire used for an ultrathin steel wire and a manufacturing method thereof. The wire has the following compositions in terms of weight percentage: 0.60 to 1.2 of C, 0.10 to 0.50 of Si, 0.01 to 0.60 of Mn, no more than 0.020 of P, no more than 0.020 of S, no more than 0.002 of Ti, no more than 0.005 of Al, no more than 0.006 of N and Fe and the balance of inevitable impurities. The manufacturing method comprises the following steps: smelting, molten iron desulfurisation and converter top and bottom blowing are carried out by adopting an ultrapure steel technique, ladle argon blowing refining and external refining are carried out by adopting low-alkalinity steel slag with 0.5 to 1.6 of CaO/SiO2; square billet is formed by casting; austenitizing with the temperature of 750 DEG C to 850 DEG C is carried out on the square billet by using a heating furnace; control rolling and control cooling treatment is carried out on the high speed wire; the rolling temperature is controlled to be 750 to 900 DEG C; and finally the wire is manufactured. The wire can effectively avoid the filament breakage in the drawing technique, and the drawn filament is not broken at least when drawn for more than 1,200,000 meters; and the wire can produce ultrathin steel wire, which has the diameter of less than 0.50 mm and has high strength and high toughness, and meets the requirements of automotive and rubber industries and the construction of roads and bridges.