After removal of resin and gutta percha under petroleum ether reflux, Eucommia ulmoides (orDuzhong) leaveswere decoctedwith distilled water and the combined extraction solution was concentrated and fractionally precipitated by adding the one-fold, twofold and threefold volumes of alcohol to obtain three groups of crude polysaccharides, PsEUL1, PsEUL2 and PsEUL3. Bio-active assay showed PsEUL1 and PsEUL3 possessed high anti-complement activities. Of them, the group of polysaccharides, PsEUL1, with the highest anti-comlement activity, was decolourized on a macro-porous resin (S-8) column and deproteinized using Sevag reagent. After dialysis, the refined PsEUL1 was applied to a diethylaminoethyl (DEAE)-cellulose anion exchange column and three polysaccharides, PsEUL11, PsEUL12 and PsEUL13, had been isolated. The further assays of anti-complement activities indicted these isolated polysaccharides have different extent of inhibitory activities, ofwhich PsEUL13 was the one with the highest activity and showed dose-effect relationships. The half inhibitory concentration, IC50, of PsEUL13 was 210 ìg/mL. The reaction with sulfuric acid and carbazole substantiated it was an acidic polysaccharide, containing 21.2% of uronic acid. The gas chromatography revealed, besides uronic acid, PsEUL13 contained L-rhamnose,D-fucose, D-arabinose, D-xylose, D-glucose and D-galactose, and their percentage composition were 11.8%, 1.6%, 37.7%, 4.2%, 10.7%and 12.8%, respectively.