A new triterpenoid named alisol O ( 1) was isolated from the rhizomes of Alisma orientalis, together with six known compounds: alisol A 24-acetate ( 2), 25-anhydroalisol A ( 3), 13 beta,17 beta-epoxyalisol A ( 4), alisol B 23-acetate ( 5), alisol F ( 6), and alisol F 24-acetate ( 7). Based on 1D and