Abstract: OBJECTIVE To investigate the effect and mechanisms of the osthole on the human breast cancer cells lines MCF-7. METHODS The human breast cancer cells lines MCF-7 were cultured in vitro and the MCF-7 cell at logarithmic growth phase was treated with different concentration of osthole(0, 25, 50, 100 mmol·L^-1) for 48 h. MTT and flow cytometric analysis were used to evaluate the proliferation, apoptosis, and membrane potential of MCF-7 cells. RT-PCR was used to examnine the p53, p21, BCL-2, Bax and CytC mRNA level. The expression of p53, p21, BCL-2, Bax and CytC in MCF-7 cell were detected by Western blotting. RESULTS Osthole treatment could induce the proliferation inhibition, apoptosis and the expression of Bax, p53, p21 and CytC with decreasing the membrane potential and the expression of BCL-2 on MCF-7 cell in a concentration dependent manner. CONCLUSION Osthole can induce the apoptosis of MCF-7 by activating p53 signaling.