In our study, luteolin has shown its apoptosis-inducing potent in HL-60 cells with its 76.5% apoptotic ratio of 100 microM treatment. When HL-60 cells were treated with 60 microM of luteolin, DNA ladders were visible at 6 h and increased from 6-12 h after treatment. Luteolin could decrease the mitochondrial membrane potential, trigger cytochrome c released to cytosol, and subsequently induce the processing of procaspase-9 and procaspase-3, which were followed by the cleavage of poly-(ADP-ribose) polymerase (PARP) and DNA fragmentation factor (DFF-45). The cleavage of the proapoptotic Bcl-2 proteins, such as Bad and Bax to produce their truncated forms, and the cleavage of the antiapoptotic Bcl-2 proteins, such as Bcl-2 and Bcl-XL, into their potent pro-apoptotic fragments were detected in our study. From the results, we suggested that the structure of luteolin contributes to its potent in inducing apoptosis in HL-60 cells, and the mitochondrial pathway might play an important role in the luteolin-induced apoptosis. The induction of apoptosis by luteolin may offer a pivotal mechanism for its cancertherapeutic and chemopreventive action.