To provide a method for preventing the overoxidation of slag and molten steel in the end period of converter blowing.

The oxygen supply rate from a top blowing lance is lowered down to 50 to 80% of the peak period of decarburization at the point of the time the [C] concn. in the molten steel attains 0.5 to 1.0wt.% in the end period of blowing of the top and bottom blowing converter. In succession, the top blowing lance is immersed right under the surface of the molten steel and the oxygen is blown into the steel bath before blowing-out at the point of the time the [C] concn. in the molten steel attains 0.2 to 0.4wt.%. The (%T, Fe) and [%O] decrease in the end period of blowing and, therefore, not only the decrease in the alloy consumption unit with an improvement in the yield of the alloy addition is made possible but the production of the highly clean steel is made possible as well.