A new compound was isolated from Smilax glabra Roxb., named isoastilbin. It was identified as 5, 7, 3', 5'-tetrahydroxyl-flavanonol-3-O-alpha-L-rhamnopyranoside by means of chemical and spectrometric analysis (UV, IR, 1H-NMR, 13C-NMR, 2DNMR and FAB-MS).