Screening of anticoagulant activity was conducted for the hot water extracts of 73 kinds of medicinal herbs, 41 kinds of Korean edible plants. and 5 kinds of sea weeds using plasma recalcification test(Tr). In the first screening several extracts of the plants, Alisma calnaliculation, Corydalis ternate. Panax notoginseng. Allium sativum, Ganoderma lucidum, Codium fragile, showed high activities. When the plants were reextracted with various solvent conditions, acidic water extracts of Codium fragile showed the highest activity in APTT. A crude polysaccharide fraction(CF-1) was prepared by methanol reflux, ethanol precipitation, dialysis and lyophilization of the acid extracts. CF-1 comprised 80.8% total sugar consisting of arabinose, galactose and glucose as the main monomers, 8.7% protein, and 13.3% sulfate. The anticoagulant activity of CF-1 was not changed by pronase digestion, but decreased by periodate oxidation, and this indicated that the anticoagulant activity was attributed to the polysaccharide portion.