A new prenylflavanone, antiarone K (1), together with seven known flavonoids, antiarones B, F～I (2～6), (±)-sigmoidin A (7), and 2-[2,3-dihydro-4-hydroxy-2-(2-hydroxy-2-propyl)-5-methoxy-1H- inden-1-yl]-1-(2,4,6-trihydroxyphenyl)ethanone (8), was isolated from the ethanolic extract of the roots of Antiaris toxicaria (Pers.) Lesch collected from Hainan. The structures were established by spectroscopic methods (IR, 1D-, 2D-NMR, and HR-ESIMS). Compounds 1 and 3 possessed inhibitory effects on Staphy-lococcus aureus, and compound 3 possessed inhibitory effects on methicillin-resistant Staphylococcus aureus (MRSA) as shown by the filter paper disc diffusion method. Compounds 1, 6～8 showed inhibitory activity towards chronic myelogenous leukemia (K562), human gastric carcinoma (SGC-7901), and human hepatoma (SMMC-7721) cell lines by MTT assay.

Key words: prenylflavanone, antiarone K, cytotoxicity, antibacterial activity, Antiaris toxicaria