Anti-coagulant activities of 25 species of medicinal plants which have been related to "blood" in ethnobotany, were evaluated by plasma recalcification time test. Among these, Artemisiae Herba showed the strongest activity. Its anti-clotting component was purified by using DEAE-cellulose, Sephadex G-75, and Sephadex LH-20 column chromatography. Its active compound has an average molecular weight of approximately $10^{4}$ and it was turned to be an acidic polysaccharide composed of galacturonic acid and rhamnose (7 : 2) by chemical analysis and spectral data.