Galactomannan with a molecular weight of 1976 kDa was isolated by hot water extraction from the locoweed (Oxytropis lanata (Pallas) DC) seeds (yield, 3.68% of the seed weight); its solutions display high viscosity: [eta] = 1697.7 ml/g and optical activity [alpha]D + 76.8 degrees. The polysaccharide consists of mannose and galactose residues at a molar ratio of 1.36 : 1. The backbone of galactomannan macromolecule is formed by 1,4-beta-D-mannopyranose residues, 73.5% of which are substituted with single alpha-D-galactopyranose residues at C-6.