This study was conducted to investigate the effects of blueberry extract on cell death, ROS and gene expression patterns associated with the anti-cancer activity in human breast cancer MCF7 cells. To accomplish this, 20 mg/mL concentration of blueberry extract was added to the cell culture for 0, 6, 12, 24 or 48 h, after which the effects were evaluated by various analyses. MTT assay showed that the cellular activities decreased rapidly during the first 12 h of treatment. During this period, dual staining with Hoechst33322 and propidium iodide also produced a similar trend in which the dead or dying cells increased sharply. Furthermore, evaluation of BrdU incorporation as an index for cell proliferation revealed a marked decrease during the first 12 h of treatment, suggesting that anticancer activity involves the inhibition of cell proliferation and induces cell death. ROS also increased according to the duration of the treatment, indicating intracellular accumulation is associated with the cell death. RT-PCR analysis revealed significant decreases in anti-apoptotic (Bax) and increases in pro-apoptotic gene expressions (Bci-2, caspase- 3, and 9) (p<0.05). Taken these together, blueberry extract induces ROS accumulation in MCF7 cells, causing inhibition of cell proliferation and eventually leading to cell death. This cell death was associated with apoptotic gene expression in blueberry-treated cells for up to 24 h.