Background: CD39 is an integral membrane protein (ectoenzyeme) that phosphohydrolyzes ATP in a Ca²⁺- and Mg²⁺-dependent fashion to yield AMP, Can be viewed as immunological switch, and is expressed in spleen, thymus, lung, and placenta, and in these organs it is associated primarily with endothelial cells and immune cell populations, such as B cells, NK cells, dendritic cells, Langerhans cells, monocytes, macrophages, mesangial cells, neutrophils, and regulatory T cells. Aim of the study is to assess the expression of CD39 on CD4⁺ CD25^high T-reg cells in patients with acute myeloid leukemia to identify its role in immunosuppressive status of AML patients. Methods: Flow cytometric analysis of T-reg cells using CD4 CD25 and CD39 in 60 AML patients and 15 apparently healthy controls with matched age and sex was done. Results: There was a significant difference between cases and controls as regards expression of CD39 on T-helper cells. A highly significant elevation of expression of CD39 has been obtained on T-reg cells in AML patients compared with Controls with increased expression of CD39 on T-reg cells than on helper T cells. Conclusion: CD39 plays a significant role in immunosuppressive status of AML patients particularly with expressing the receptor of α chain of IL-2 (CD25)