PURPOSE: To substantially prevent the rephosphorization in a ladle by a method wherein a slag diluting agent consisting of an inorganic refractory material is added in the final period of the blowing process in a converter or during tapping of steel from the converter into a ladle so as to regulate the concentration of P2O5 in a slag to be not higher than a predetermined value.

CONSTITUTION: The slag diluting agent consisting of an inorganic refractory material is added either into the converter in the final period of the blowing process in a basic oxygen converter or into the ladle during tapping of the molten steel from the converter into the ladle, so as to regulate the P2O5 concentration in the slag to be not higher than 1.0%, particularly 0.8% or below. As the inorganic refractory material, one that contains no phosphorus component, for example, a brick layer of the converter, gravel or the like is used. By the regulation of the P2O5 concentration in the slag, P2O5 in the slag is prevented from being further reduced in the deoxidizing process conducted in the ladle for producing a killed steel, so that the rephosphorizing phenomenon is prevented, that is, the P concentration in the molten steel in the ladle is prevented from increasing.