A water-soluble polysaccharide, PGAW1, with an average molecular mass of 9.2 kDa determined by high performance gel permeation chromatography (HPGPC), was isolated from radix of Platycodon grandifloram. Monosaccharide composition analysis indicated that PGAW1 contains Ara and Gal in the molar ratio of 1.42:1.0. Using methylation analysis, partial hydrolysis, endo-1,4-beta-D-galactanase digestion. NMR and ESI-MS. PGAW1 was determined to possess a backbone consisting of 1,4-and 1,6-linked galactopyranosyl residues, with branches attached to O-3 of 1,6-linked galactose residues. By the chlorosulfonic acid-pyridine method we produced a sulfated derivative of PGAW1, Sul-wl, with a substitution degree of 1.52. The substitution was to O-6 on 1,4-linked Gal residues according to the C-13 NMR spectra, Bioactivity test showed that Sul-wl could inhibit tube formation by human microvascular endothelial cells (HMEC) in a dose-dependent manner.