Crude ginseng saponin fraction reduced the production of thromboxane $A_2$in the lipopolysaccharide-stimulated macrophages. Several kinds of crude saponins showed variant potency that might be caused by the compositional difference of ginseng saponins. From the metabolic labeling experimental data, this reduction of thromboxane $A_2$formation, at least in part, resulted from the reduction of protein synthesis of inducible isozyme of cyclooxygenase(COX-2). This activity may be resulted from the fact that ginseng saponins have steroidal moiety in their structures.