An object of the present invention is to provide a method for producing a great deal of inexpensive high purity silicon useful in a solar battery. Disclosed is a method for producing the high purity silicon by migrating impurities in molten silicon to slag including the step of feeding an oxidizing agent to the molten silicon together with slag, wherein the oxidizing agent is a material comprising as a primary component at least one of the following materials: alkali metal carbonate, hydrate of alkali metal carbonate, alkali metal hydroxide, alkaline-earth metal carbonate, hydrate of alkaline-earth metal carbonate or alkaline-earth metal hydroxide.