Abstract: Objective: to isaolate, purify and structurally characterize a water-soluble polysaccharide from the whole herbs of Ligularia hodgsonii. Methods: crude polysaccharide named as LW was extracted from Ligularia hodgsonii. A ploysaccharide fraction named as LW21 was obtained after acidic ethanol fractionation and DEAE-Sephadex A-25 gel filtration. The purity of LW21 was identified by paper chromatography, Sepharose CL-4B chromatography and cellulous acetate electrophoresis, and its structure was analyzed by HIO4 oxidation, Smith degradation, methylation, IR, NMR, GC and GC-MS. Results: LW21 was a homogenous polysaccharide. LW21 was composed of rhamose (Rha), arabinose (Ara), mannose (Man), glucose (Glc) and galactose (Gal) with a molar ratio of 7.4: 11.9: 25.7: 40.0: 14.9. Its average molecular weight was 110 kD. Its main chain was made up of β-(1→2)-linked or β-(1→6)-linked Man, and β-(1→2)-linked orβ-(1→6)-linked Glc residues. The β-(1→2)-linked Man was substituted at 2－O and 4－O; β-(1→6)-linked Man was substituted at 3－O and 6－O; and β-(1→2)-linked Glc was substituted at 6－O; β-(1→6)-linked Gal was substituted at 2－O. The side chain was composed of Rha, Ara and Gal. The non-reduced end was composed of Gal, Ara, Rha and Glc. Conclusion: LW21 is a new polysaccharide isolated from Ligularia hodgsonii for the first time.

Key words: Ligularia hodgsonii, polysaccharide, methylation analysis, structural analysis