Objective:To investigate the expression levels of CD4+ CD25+ FOXP3+ Treg cells and interleukin(IL)-10 in serum of patients with myelodysplastic syndrome (MDS) - refractory anemia (RA) and refractory hematopenia with multilineage dysplasia (RCMD), and to evaluate the effect of cyclosporine on CD4+ CD25+ FOXP3+ Treg cells in MDS patients.Methods:From January 2016 to January 2018, 25 MDS-RA and RCMD patients and 13 healthy controls were selected from people′s Hospital of Xinjiang Uygur Autonomous Region for retrospective analysis.The expression of CD4 + CD25 + Foxp3 + Treg and IL-10 in peripheral blood samples were detected by flow cytometry and enzyme-linked immunosorbent assay.The expression of CD4 + CD25 + Foxp3 + Treg and IL-10 in MDS-RA and RCMD patients before and 6 months after the treatment with CSA based immunosuppressive regimen was detected.Results:Of the 25 patients, 13 (52%) were effective and 12 (48%) were ineffective.The proportion of CD4 + CD25 + Foxp3 + Treg in CD4 + T cells of MDS group was significantly higher than that of healthy control group [(0.37 ± 0.10)% and (0.12 ± 0.06)% respectively, t= 2.02, P< 0.001]. The level of IL 10 in MDS group was significantly higher than that in healthy control group ((7.16±1.27) μg /L and (2.75 ± 1.06) μg /L, t= 2.03, P< 0.001). The ratio of CD4 + CD25 + Foxp3 + Treg cells in MDS group was lower than that in MDS Group ((0.15±0.06)% and (0.26±0.08%), t= 1.71, P< 0.001), and the level of IL 10 in MDS group was lower than that in MDS Group ((3.22±1.01) μg /L and (4.25±1.22) μg /L, t= 2.06, P= 0.030). The proportion of CD4 + CD25 + Foxp3 + Treg in peripheral blood of 25 MDS patients was positively correlated with the level of IL-10 expression ( r= 0.35, P= 0.02). Conclusion:The expression of CD4+ CD25+ FOXP3+ Treg cells and IL-10 increased in MDS patients increased, but decreased after cyclosporine treatment.