The anti-cancer effects of Angelica keiskei ethanol extract were evaluated in human breast cancer MDA-MB-231 cells. The concentrations of extract were 1, 2, 3, 4 and 5 mg/mL. Dose-dependent reductions in the number of cells with altered cell shape and pyknotic nuclei were observed at 48 h after treatments. MTT assay also exhibited a similar dose-dependent reduction in mitochondrial reductase activity (p<0.05), in particular, with a rapid reduction in the activity of the 5 mg/mL group. Analysis of cell death with propidium iodide (PI) staining revealed only a slight increase in cell death in the 5 mg/mL group. Analysis of bromodeoxyuridine (BrdU) incorporations also showed a dose-dependent reduction in cell proliferation (p<0.05). Finally, increases in total radical oxygen species (ROS) accumulation in cells, as revealed by DCF-DA staining, were observed in the treated groups in a similar dose-dependent fashion (p<0.05). These results indicate that Angelica keiskei ethanol extract exhibiting anti-cancer effects in MDA-MB-231 cells causes multiple changes in cell shape, enzyme activity, and ROS accumulation, thereby inducing cell death.