To extract sulfur from sulfur-containing slag in a short time without carrying out high temperature treatment, to separate and remove sulfur from hot metal desulfurization slag, and to recycle the slag thereof.

At least one kind of slag selected from hot metal desulfurization slag and air-cooled blast furnace slag is immersed in an aqueous solution of pH 13.0 or more, whereby the sulfur content in the slag is dissolved in the aqueous solution and extracted. Hot metal desulfurization slag from which sulfur has been extracted by this extraction method is used as a desulfurization flux in hot metal pretreatment or as a raw material for sintering.