By the hot water extraction method, galactomannan was extracted (4.5% yield of the seed mass) from the seeds of Chinese honey locust (Gleditsia sinensis Lam). It had a molecular weight of 1230 kDa, and its solutions had a high viscosity [eta] of 1064 ml/g and optical activity [alpha]D + 21.4 degrees. The polysaccharide consists of mannose and galactose residues in the molar ratio 2.69 : 1. In the galactomannan macromolecule the backbone is formed by 1,4-beta-D-mannopyranose residues, 37% of which are substituted by alpha-D-galactopyranose at C-6. By 13C-NMR-spectroscopy, fragments of differently galactose-substituted mannobiose units were found to be in the galactomannan being studied: Man-Man, (Gal)Man-Man, and Man-Man(Gal) in the ratio of 0.23 : 0.47 : 0.30.