The methanol extract of dried fruits of Odyendyea gabonensis afforded one new quassinoid [(-)-odyendanol (1)], one new canthin-6-one alkaloid [9-hydroxy-5-methoxycanthin-6-one (4)], and two new steroids [22E, 24R-stigmasta-5,22-diene-3,7-dione (7) and 22E,24R-stigmast-22-ene-3,7-dione (8)] along with fourteen known compounds. The structures of all compounds were established by analyzing the spectroscopic data. The (1)(3)C-NMR values of (-)-odyendene (2) and (-)-odyendane (3), as well as the single-crystal X-ray structure of 5-methoxycanthin-6-one (6) are also reported.The oxidative burst inhibitory activity of pure compounds 1-12 was determined by the chemoluminescence assay, and cytotoxic activities of compounds 2-6 against the human prostate cancer cell PC-3 line were evaluated. Compounds 1-6 exhibited a clear suppressive effect on the phagocytosis response upon activation with serum-opsonized zymosan in the range of IC(5)(0) = 0.9-2.0 microM versus ibuprofen with IC(5)(0) = 12.1 microM, while all canthin-6-one alkaloids (4-6) displayed moderate cytotoxic activity against the human prostate cancer cell PC-3 line, with IC(5)(0) values ranging from 13.5-15.4 microM versus doxorubicine with IC(5)(0) = 1.5 microM. CI - Georg Thieme Verlag KG Stuttgart . New York.