AIM: The present investigation aimed to examine the therapeutic potential of the new coumarin derivative bis(4-hydroxy-2H-chromen-2-one) coumarin (4HC) against breast cancer. MATERIALS AND METHODS: For this purpose, the effects of 4HC treatment on the proliferation of MCF-7 breast cancer cells and on MCF-10a non-cancerous cells were evaluated using a fluorescent assay. Cell cycle distribution and apoptosis were measured by image cytometry. The expression level of aromatase (CYP19A1) and apoptosis-related genes were determined by real-time PCR. RESULTS: MCF-7 mammary cancer cell proliferation was significantly decreased within 24 h after treatment with 4HC at 50 muM, while no effect was observed on the viability of MCF-10a non-cancerous mammary cells. 4HC also increased the percentage of the cells in the G2/M phase, inducing apoptosis. Real-time PCR revealed that 4HC induced MCF-7 mortality through an up-regulation of Bax and a down-regulation of Bcl-2, resulting in an increase in caspase-3 gene expression. The increased expression of apoptosis-related genes was accompanied by a decrease in CYP19A1 gene expression. CONCLUSION: 4HC selectively inhibits proliferation of MCF-7cells in vitro. Moreover, 4HC has inhibitory effects on aromatase gene expression and promoting effects on apoptosis, in MCF-7 cells.