A xanthone derivative, named gaboxanthone (1), has been isolated from the seed shells of Symphonia globulifera, together with known compounds, symphonin (2), globuliferin (3), guttiferone A (4), sistosterol, oleanolic acid and methyl citrate. The structure of the compound was assigned as 5,10-dihydroxy-8,9-dimethoxy-2,2-dimethyl-12-(3-methylbut-2-enyl) pyrano [3,2-b]xanthen-6(2H)-one, by means of spectroscopic analysis. The anti-plasmodial and antioxidant activities of the phenolic compounds were evaluated, respectively, in culture against W2 strain of Plasmodium falciparum and using the free radical scavenging activity of the DPPH radical, respectively. Compounds 1-4 were found to be active against the Plasmodium parasites (IC(50) of 3.53, 1.29, 3.86 and 3.17 microM, respectively). Guttiferone A (4) showed a potent free radical scavenging activity compared to the well-known antioxidant caffeic acid.