Breast cancer is the most frequent cancer among women, impacting 2.1 million women each year, and also causes the greatest number of cancer-related deaths among women .Nigella sativa L is an herbaceous, Order of the Ranunculales and one-year-old plant. This plant has valuable components such as thymoquinone, which possesses anti-cancer properties. The aim of this study was evaluation and comparison of the effect of alcoholic extract Nigella sativa L on Breast cancer cells and normal Bone Marrow-Derived Stem Cells. Human Breast cancer cell line MCK-7 and normal Bone Marrow-Derived Stem Cells were cultured in vitro and treated with different concentrations of alcoholic extract Nigella sativa L for 24 hours. The MTT assay was used to determine cell viability. Alcoholic extract Nigella sativa L in concentrations of 950 and 1250 µg/ml had killed both of cells at 24 hours after treatment and caused morphological changes in cells which were more obviously in cancer cells. Alcoholic extract Nigella sativa L in concentrations of 650 µg/ml killed 50 % cancer cells while that was little effect on Bone marrow stem cells. Cytotoxicity effect alcoholic extract Nigella sativa of on Breast cancer cells was more than its effect on normal Bone marrow stem cells and can be regarded as a safe anticancer medicine.