The behaviors of desiliconization of the hot pig iron by adding the solid iron oxide as a desiliconizing agent were studied. Even when small amount of iron oxide is added, the degree of desiliconization can be reached to 70% under the condition of slag with the basicity over 1.0. During desiliconizing treatment, the competiting reactions such as demanganization and decarburization are suppressed in the above slag condition. In (FeO) content less than 5%, the distribution ratio of silicon between slag and metal is approximately in agreement with the equilibrium value.