Breast cancer is the most commonly diagnosed cancer in women in the world and is one of the leading causes of death due to cancer. Health benefits have been linked to additive and synergistic combinations of phytochemicals in fruits and vegetables. Nigella sativa has been shown to possess anti-carcinogenic activity, inhibiting growth of several cancer cell lines in vitro. However, the molecular mechanisms of the anti-cancer properties of Nigella sativa phytochemical extracts have not been completely understood. Our data showed that Nigella sativa extracts significantly inhibited human breast cancer MDA-MB-231 cell proliferation at doses of $2.5-5{mu}g/mL$ (P<0.05). Apoptotic induction in MDA-MB-231 cells was observed in a dose-dependent manner after exposure to Nigella sativa extracts for 48 h. Real time PCR and flow cytometry analyses suggested that Nigella sativa extracts possess the ability to suppress the proliferation of human breast cancer cells through induction of apoptosis.