The chemical structure of gleditsia saponin C (GS-C), a major triterpenoid saponin of the fruit capsule of Gleditsia japonica Miq. (Leguminosae), comprised echinocystic acid, eight sugar units and two monoterpenyl groups ((+)2,6-dimethyl- and (+) 2-hydroxymethyl-6-methyl-6-(S)hydroxy-2- trans-2,7-octadienoyl groups). Methylation analysis of GS-C followed by determination with gas-liquid chromatography and mass spectrometry showed that the monoterpenyl moieties attach to the 2 and 3-positions of terminal L-rhamnose of the C-28 oligoside portion.