Phytochemical study of the ethanol extract of the seeds of Aesculus chinensis led to the isolation of a new triterpenoid saponin (6), together with five known triterpenoid saponins (1-5). The structure of the new compound was elucidated on the basis of spectral data to be 21,28-di-O-acetylprotoaescigenin-3-O-[beta-D-glucopyranosyl(1-2)][beta-D-glucopyranosyl(1-4)]-beta-D-glucopyranosiduronic acid (aesculiside A, 6). The antiinflammatory activities of the four main saponins (1-4) were compared with those of total saponin extracts, and single saponins showed more potent activity than total saponin extracts in mice.