PURPOSE: To make possible the desulfurization down to a target S content rapidly with less Al consumption by adding the specific amount of powder Al together with powders of Al2O3 and CaO to molten iron at the time of desulfurizing the molten iron by CaO and CaC2.

CONSTITUTION: In the case of desulfurizing and refining molten iron outside the furnace, powder Al is blown together with powder Al2O3 or powder CaO or a mixture of Al2O3 and CaO into the molten iron through an immersion nozzle by using a carrier gas such as N2. In this case, the Al is so added that the Al concentration in the molten iron is expressed by the following formula. Al concentration=(0.01W0.1)×(Si concentration in molten iron)+(0.2W1.0)×(S concentration to be desulfurized). When the Al concentration reaches the above-mentioned concentration, the desulfurizer comprising the mixture of CaC2 and CaO is added to rapidly desulfurize the molten iron down to the target S content.