Background and Objective: Chronic myeloid leukemia (CML) is a malignant clonal disorder of hematopoietic stem cells which results in increase of myeloid and erythroid cells and platelets in the peripheral blood and hyperplasia in bone marrow. This research evaluated the cytotoxic effect of aqueous, methanolic and ethanolic extracts of M. spicata leaves on K562 cell line as a model of chronic myeloid leukemia. Materials and Methods: In this experimental trial, leaves of M. spicata were collected from Booin city and extracted using soxhlet method. K562 cells were cultured and treated with concentrations of extracts (12.5-150μg/ml). Cytotoxicity of M. spicata extracts against K562 leukemia cells was estimated by the MTT test method. The absorbance was measured using ELISA plate reader at 540 nm. Results: Ethanolic extract showed the highest cytotoxic effect (IC50=75 μg/ml) whereas aqueous extract showed the least cytotoxic effect (IC50=150 μg/ml) among the extracts. Methanol extracts showed the cytotoxic effect with IC50=100 μg/ml on K562 cell line. Aqueous and alcoholic extracts exhibited a dose-dependent cytotoxic effect on K562 cell line. Conclusion: Considering the cytotoxic effects of aqueous and alcoholic extracts of M. spicata leaves on K562 cells, this plant can be considered as a potential candidate for further studies in the treatment of CML.