A new 3,28 - bidensmosidic triterpenoid saponin was isolatde from the ethanolic extract of the root of Dipsocus japonicus and its structure established as 3-O-α-L- rhammopyranosyl (1→3) -β- D - glycopranosyl (1→3) -α- L - rhammopyranosyl(1→2) -α-L- arabinopyranosyl - hederagenin -28 -O -β- D -glycopranoside. The results obrained showed that the chemical structure of oligosaccharide chains of the saponin could be elucidated by the combination of 1D - SEMDY, NOE difference spectroscopy in rotating frame and selective long - range DEPT techniques, without having recourse to chemical degration or modification. Complete assignments of severely overlapping proton resonance of the sugar residues were obtained.

Key words: DIPSACUS ASPER, TRITERPENE, SAPONINS, PYRANE P, RHAMNOSE, GLUCOSE, ARABINOSE