Breast cancer is the second most pervasive cancer among women. Breast cancer is a worldwide epidemiological problem which the current remedies cannot heal it effectively and has unwanted side effects. Therefore, attempt to produce more effective medicine with less toxicity is essential. Ferula gummosa is anti-cancer, anti-spasm, anti-paroxysm, antiseptic and laxative and it is tonic for stomach, reconstructs surface scars, and causes more milk producing in breasts. Since, its anti-tumorous effects have not been studied on the breast cells; the cellular toxicity effect of its ethanolic extract was investigated in this study. To investigate the preventing effects of F. gummosa ethanolic extract on cellular growth, we have used the MCF7 (Human Caucasian breast adenocarcinoma) cell line which has been cultivated in RPMI environment containing cow's embryo serum and antibiotic. Then we treated these cells in different concentrations of F. gummosa ethanolic extract (0.165, 0.312, 0.625, 1.25, 2.5, 5, 7.5, and 10 mg/ml) for 72 hours. The amount of cell viability was determined by MTT method. Ethanol extract of F. gummosa has a significant cellular toxicity effect on the MCF7 cell line in 0.625, 1.25, 2.5, 5, 7.5, and 10 mg/ml densities after 72 hours compare with control group, and the calculated IC50 for F. gummosa extract was 1.765 mg/ml. The results suggest that ethanol extract of F. gummosa has preventing effect on the cellular growth of MCF7 cellular class.