Background: Plants are an important natural source of compounds used in cancer therapy. Pancratium maritimum contains potential anti-cancer agents such as alkaloids. In this study, we investigated the anti-proliferative effects of P. maritimum extracts on MDA-MB-231 human epithelial adenocarcinoma cell line and on normal lymphocytes in vitro. Methods: Leaves, flowers, roots, and bulbs of P. maritimum were collected and their contents were extracted and diluted to different concentrations that were applied on MDA-MB-231 cells and normal human lymphocytes in vitro for different intervals. Cells viability, proliferation, cell cycle distribution, apoptosis, and growth were evaluated by flow cytometry and microscopy. Parametric unpaired t-test was used to compare effects of plant extracts on treated cell cultures with untreated control cell cultures. IC50 was also calculated.Results: P. maritimum extract had profound effects on MDA-MB-321 cells. It inhibited cell proliferation in a dose- and time-dependent manner. The IC50 values were 0.039, 0.035, and 0.026 mg/ml after 48, 72, and 96 hours of treatment with 0.1 mg/ml concentration of bulb extract, respectively. Those values were 0.051 and 0.03 mg/ml after 72 and 96 hours for root extract, respectively, and 0.048 mg/ml after 96 hours for flower extract. There were no significant effects of P. maritimum bulb extracts on normal lymphocytes proliferation.Conclusion: P. maritimum extract has anti-proliferative effects on MDA-MB-231 cell line in vitro. The effects imply the involvement of mechanisms that inhibits cell growth and arresting cells at S and G2/M phases. Cyclin B1, Bcl-2, and Ki67 expression was also affected.