A method for the desulfurization of molten pig iron which comprises submerging a submersion-type free board and an injection lance in molten pig iron within a ladle and blowing an inert gas and CaO powder into the molten pig iron through the injection lance to desulfurize the molten pig iron, and which is provided with the step of adding metallic Al to the surface of the molten pig iron after theoxygen partial pressure within the submerged free board has been lowered to 0.1MPa or below by blowing the inert gas into the submerged free board and before 30mass% of the total CaO powder used has been blown into the molten pig iron.