In this study, we investigated the effects of the ethanol extract of aerial parts of Raphanus sativus L. (ERL) on breast cancer cell proliferation and gene expression associated with cell proliferation and apoptosis in MDA-MB-231 human breast cancer cells. The MDA-MB-231 cells were cultured in the presence or absence of various concentrations (100, 200, or 300 µg/mL) of ERL. ERL significantly decreased cell proliferation after 48 h of incubation ( P < 0.05). The protein and mRNA expression of ErbB₂ were decreased significantly in a dose-dependent manner ( P < 0.05). The protein expression of ErbB₃ was decreased significantly at an ERL concentration of 300 µg/mL ( P < 0.05), and mRNA expression of ErbB₃ was decreased significantly in a dose-dependent manner ( P < 0.05). The protein expression of Akt was decreased significantly at the ERL concentration of 200 µg/mL ( P < 0.05), and the protein expression of pAkt was decreased significantly in a dose-dependent manner ( P < 0.05). The mRNA expression of Akt was decreased significantly at the ERL concentration of 200 µg/mL ERL ( P < 0.05). The protein and mRNA expression of Bax were increased significantly at ERL concentrations of 200 µg/mL or higher ( P < 0.05). The protein expression of Bcl₂ was increased significantly at ERL concentrations of 100 µg/mL or higher ( P < 0.05), and mRNA expression of Bcl₂ was increased significantly at an ERL concentration of 300 µg/mL ( P < 0.05). In conclusion, we suggest that Raphanus sativus , L. inhibits cell proliferation via the ErbB-Akt pathway in MDA-MB-231 cells.