The saponin fraction from the seeds of the tea plant, Camellia sinensis L. var. assamica PIERRE cultivated in Sri Lanka, was found to show a potent protective effect on gastric mucosal lesions induced by ethanol in rats. Nine new acylated polyhydroxyoleanene-type triterpene oligoglycosides called assamsaponins A-I were isolated from the active saponin fraction together with three known saponins, theasaponin E₁ and E₂ and camellias-aponin B₁. The structures of assamsaponins A-E were elucidated on the basis of chemical and physicochemical evidence. Theasaponin E₁ exhibited potent gastroprotective activity.