To provide a dephosphorization method of the hot metal in which the dephosphorization speed is high, the dephosphorization efficiency is high, and the cost is low.

(1) In performing dephosphorization by top-blowing oxygen in a furnace of a top-blown converter type, the hot metal is dephosphorized by controlling the slag composition to be Al2O3=2-15%, T, Fe=3-25%, CaCl2=2-10%, and alkalinity = 1.2-3.0. (2) In forming the slag, one or more kinds of the converter slag for CaO and SiO2 source, and one or more kinds of continuous casting slag and ingot making slag as Al2O3 source, and one ore more kinds of iron ore and iron scale as the iron oxide source, and one or more kinds of ammonium soda ash as CaCl2 source and the by-product in manufacturing calcium chlorate are used for the flux for dephosphorization.