This study was aimed to investigate the inducing-apoptosis effect of brucine on human monocytic leukemia cell line THP-1 cells and its possible mechanism. The inhibition effect of brucine on growth of THP-1 cells was measured by CCK-8 method. Morphological changes of THP-1 cells treated with brucine was detected by acridine orange/ethidium bromide (AO/EB)double staining. Annexin-V/PI double labeling method was used to assay the apoptosis rate of THP-1 cells. The effect of brucine on THP-1 cell cycle distribution was detected by PI single staining. RT-PCR was used to detect the expression of BCL-2 and BAX. The results showed that the brucine could inhibit the THP-1 cell growth in concentration and time-dependent manners at the range of 50 to 400 µg/ml. The cells stained with AO/EB revealed that the brucine induced the nuclear chromatin condensation. After the THP-1 cells were treated with brucine of 400µg/ml for 48 hours, most nucleic were stained as orange-red, and condensed, displaying the late apoptotic cell morphology. Annexin-V/PI detection showed that brucine could induce apoptosis of THP-1 cells in a concentration-dependent manner. Compared with the control group, more cells in brucine-treated group were arrested at G0/G1 phase in a concentration-dependent manner. RT-PCR detection revealed that the expression of BCL-2 was down-regulated strikingly and BAX was up-regulated. It is concluded that brucine can efficiently inhibit cell growth and block THP-1 cells in G0/G1 phase. The mechanism of THP-1 cell apoptosis induced by brucine may be related to the inhibition of BCL-2 and activation of BAX.