Objective: The study was aimed to evaluate the cytotoxic activity of acetone extract of leaves, flower and body of Euphorbia macroclada boiss on human breast cancer cell line (MCF-7). Material: The cells were plated at a cell density of 1x10(5) cells in 96-well plates and grown with DMEM medium containing supplemented with 10% FBS and 1% penicillin. The cells were treated by different concentrations of acetone extract of Euphorbia macroclada boiss (10-1000 mu g/mL) during 24, 48 and 72 h. The cytotoxic activities of the tested compounds were determined by cell proliferation analysis using standard (3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Results: After the evaluation of cytotoxicity assay results, it is determined that flower and body parts have a significant cytotoxic effect on MCF-7 breast cancer cell line. The values that obtained reading at 570 nm spectrophotometrically, were analyzed with GraphPad Prism7 and IC50 growth inhibition values was determined. Conclusion: The results of MTT assay showed that leaves, flower and body significantly reduced % cell viability comparative to the control. It was also shown that body had more growth inhibitory effect on MCF-7 cell compared to the leaves part.