A new xanthonoid, tomentonone [la], together with zeyloxanthonone [lb], calozeyloxanthone [3], and five other hydroxylated xanthones, was isolated from the bark of Calophyllum tomentosum. The structure of la has been established as [1,2,3,4-tetrahydro-6,8 dihydroxy-1,l-bis( 3-methylbut-2-enyl)-xanthen-2,9-dione) by spectroscopic and chemical methods. Xanthones, inspiteoftheir restricted occurrence in the plant kingdom, are reported to possess antileukemic, antitumor, antiulcer, antimicrobial, antihepatotoxic, and CNS-depressant activities (1-3). Plants belonging to the family Guttiferae are known to elaborate prenylated xanthones in addition to simple oxygenated xanthones (4). In our search for bioactive compounds, phytochemical investigation of the stem bark of Calophylhm tomentosum T. Anders (Guttiferae) was undertaken. Isolation of betulinic acid, friedelin, taraxerone, sitosterol, and calabaxanthone from the bark of C. tomentosum has been described in the literature (5-7). Herein we report the isolation and characterization of tomentonone {la], a new xanthonoid, along with two rare prenylated xanthonoids, zeyloxanthonone (syn. wightianone) Ilb7 and caloteyloxanthone 137, and several other compounds.