Introduction: Thromboembolic conditions in cancer patients undergoing chemotherapy are 4 to 7 times higher than in control patients. The aim of this study is to evaluate the procoagulant activity of microparticles (MPs) expressing phosphatidylserine (PS) derived from breast cancer cell line MDA-MB-231 treated with Adriamycin. Methods & Materials: In this experimental study, MDA-MB-231 breast cancer cells were treated with concentrations of 0. 5, 1, and 2 μ, M adriamycin for 24 and 48 hours. Using centrifugation technique, the MPs in the cell culture medium were separated from other contents and flow cytometry was used to count and determine the MPs phenotype. At the end, the statistical analysis of the data was done SPSS software version 23 (IBM, USA). Results: The total number of MPs increased by 11. 3 and 11. 8 times in 24 and 48 hours treated and 2 μ, M dose respectively (p<0. 001). Almost 49% of all MPs were positive in terms of Annexin V marker, which is an indicator of procoagulant MPs. In the culture medium treated with a dose of 2 μ, M, the procoagulant activity of MPs at 24 and 48 hours was 42 ±,5. 9 nM and 58 ±,6. 8 nM PS, respectively, which was more than 14 compared to the control groups. They had an increase (p<0. 001). Conclusion: Adriamycin increases the procoagulant activity of tumor-derived MPs, which can be one of the important and effective reasons for causing thromboembolic conditions in patients undergoing chemotherapy.