Gaudichaudione A, a cytotoxic xanthone obtained from Garcinia gaudichaudii, displayed strong growth inhibitory effects against Jurkat human leukemic cells, parental murine leukemic P388 and P388/DOX-resistant cell lines, and exhibited similar cytotoxicity against P388/DOX as well as P388, but was less toxic toward normal human Chang liver cells. A variety of apoptotic events induced by gaudichaudione A at the mitochondria) and nuclear levels has been characterized. It appears that gaudichaudione A induced a collapse of the mitochondrial transmembrane potential. Caspase-3 was activated and induced internucleosomal DNA fragmentation and externalization of PS residues. The apoptotic features were also observed in ultrastructural studies.