Abstract: Expansion of expansive soils may cause damage to structures. The slag mixture-a newmaterial for improving the engineering properties of expansive soils is introduced. It has been applied successfully to the expansive soil slopes for protection. The mixtures of expansive soils and slag mixture mixed in proportion, are lower in cost than mortar slabstones or concrete as slope protection materials. The cost may be reduced by one half to one-third. It has higher compressive strength （unconfined com-pressive strength is 2 10MPa）, simple and quick in construction.