To provide a method for treating lead slag, which can reduce the amount of drainage generated from lead slug and remove copper from the lead slag.

The method for treating lead slag includes the steps of: adding a sulfuric acid, a ferric sulfate and air into the lead slag to leach out copper in a leaching solution; performing solid-liquid separation to the leaching solution by filtering the solution; performing sulfurization treatment to the leaching solution after the solid-liquid separation by adding a sulfidizing agent to the solution to generate a copper sulfide; and performing solid-liquid separation by filtering a sulfurized solution that is obtained after the sulfurization treatment to remove the copper sulfide from the sulfurized solution.