A potent immuno-stimulating activity was detected from the watersoluble and ethanol-precipitated crude extract (AG-1) of the root of Angelica gigas Nakai. The crude extract was fractionated into two fractions, an acidic AG-2 and a neutral AG-3 fraction by DEAE-cellulose adsorption. The two fractions contained polysaccharides of which M.W. were 10 Kdal and >2,000 Kdal respectively, proteins, and various inorganic components. The immunostimulating activities of two fractions were not reduced by proteinase K, acid or alkali treatment. The polysaccharides obtained from the root of A. gigas were mainly composed of arabinose, galactose, and galacturonic acid. These results indicated that immuno- stimulating components of the root of A. gigas was a kind of pectic polysaccharides or arabinogalactans.