The isolation and characterization of a novel triterpene glycoside from the sea cucumberCucumariafrondosa, collected from the Gulf of St. Lawrence, are described. Physico-chemical data obtained on the underivatized saponin are presented in support of structure1for frondoside A. The structure is characterized by the presence of a branched oligosaccharidic chain composed of five units. The holostane-type aglycone features an endocyclic double bond at position C-7,8 and a β-acetoxy group at C-16.Keywords: triterpene glycoside;Cucumariafrondosasaponins; saponins, triterpene from holothurians; holothurian saponins; echinoderm triterpene saponins.