To allow desulfurization for molten iron by which molten iron can be desulfurized with high efficiency and high operability, and the molten iron can rapidly be fed to a converter in the following stage.

The desulfurizing agent for molten iron has a composition containing 5 to 30% metal Mg powder, 50 to 90% CaO and 4 to 10% calcium aluminate, and the balance inevitable impurities, and in which CaO and calcium aluminate are blended in the ratio of 3 to 15. Further, in the desulfurization method for molten iron, the desulfurizing agent is blown so that the feed rate of the metal Mg powder therein is controlled to 5 to 25 kg/min by using a laddle for separating molten slag, on blowing-off of molten iron after the treatment, the laddle is decanted so that the molten iron is discharged from a blow- off port of molten iron, and on blowing-off of desulfurized slag, the laddle is decanted so that the slag is discharged from a slag discharge port provided in the opposite direction.