Kupchan and associates (1) isolated eight quassinoids, including the antileukemic bruceantin that reached phase II clinical trials at the National Cancer Institute, from the Ethiopian Brucea antidysenterica Mill. (Simaroubaceae). Recently we reported on the isolation and structural elucidation of four new antileukemic quassinoids, bruceantinoside A and B (2), bruceanol A and B (3), and cytotoxic antileukemic alkaloids (4,5) from the stem of B. antidysenterica. We now describe the isolation and characterization of a new, potent, cytotoxic quassinoid, bruceanol C [1], from this same plant. Bruceanol C [1] was obtained as a colorless amorphous powder. The ¹H-nmr (Table 1) signals for H-1, H-3, H-7, H-12, H-15, Me-4, Me-10, and OMe of 1 were coincident with those of bruceanol B [2] and isobruceine B [3]. On the other hand, the signals for H-2', Me-3', Me-4', and OAc-4' of 1 were very similar to those of yadanzioside K [4] (6). Two singlets for Me-4' at 1.51 and 1.53 ppm are due to the OAc substitution at 4' position of the C-15 side chain. The ¹³C-nmr signals for C-1 to Me-10 of 1 coincided with those of 2 and 3. On the other hand, the signals for C-1'-C-9' of 1 were coincident with those of 4. These data led to the assignment of structure 1 for bruceanol C. The ir spectrum also supported this structure. From this structure, the molecular formula should be C30H38O13 (mol wt 606); however, eims showed the highest peak at m/z 546 instead of m/z 606. High resolution eims showed a peak at m/z 546.2105, which corresponds to C28H34O11 ([M - C2H4O2]+), indicating the elimination of HOAc from 1.