6,8-Dihydroxy-7-methoxy-1-methyl-azafluorenone (DMMA), a purified compound from Polyalthia cerasoidesroots, is cytotoxic to various cancer cell lines. The aims of this study were to demonstrate the type of cancercell death and the mechanism(s) involved. DMMA inhibited cell growth and induced apoptotic death in humanleukemic cells (HL-60, U937, MOLT-4), human breast cancer MDA-MB231 cells and human hepatocellularcarcinoma HepG2 cells in a dose dependent manner, with IC50 values ranging between 20-55 μM. DMMA alsodecreased cell viability of human peripheral blood mononuclear cells. The morphology of cancer cells inducedby the compound after staining with propidium iodide and examined under a fluorescence microscope wascondensed nuclei and apoptotic bodies. Mitochondrial transmembrane potential (MTP) was decreased after 24hexposure in all five types of cancer cells. DMMA-induced caspase-3, -8, and -9 activity was strongly induced inhuman leukemic HL-60 and MOLT-4 cells, while in U937-, MDA-MB231- and HepG2-treated cells there waspartial induction of caspase. In conclusion, DMMA-induced activation of caspase-8 and -9 resulted in executionof apoptotic cell death in human leukemic HL-60 and MOLT-4 cell lines via extrinsic and intrinsic pathways.