Objective To investigate the effects of leptin on Treg cells and the possible mecha-nism. Methods Leptin-deficient ( ob/ob) mice and homologous wild-type mice were used in this study. The percentages of Treg cells in spleen tissues and peripheral blood samples were measured by flow cytometry ( FCM) . Differences in Treg cell functionality were compared between the two groups. Splenic CD4+T cells, separated from the ob/ob mice and the wild-type mice by magnetic beads, were respectively cultured with leptin and anti-leptin neutralization antibody to evaluate the effects of leptin on Treg cells. Quantitative real-time PCR was performed to analyze the expression of Treg cell-related cytokines at transcriptional level. The levels of IL-10 and TGF-β in the supernatants of CD4+T cell culture were measured with Luminex technolo-gy. Results Compared with the wild-type mice, the ob/ob mice showed higher percentages of Treg cells in both peripheral blood samples and spleen tissues [(11. 56 ± 0. 72)％ vs (5. 47 ± 0. 81)％, (10. 16 ± 0.93)％ vs (6.29±0. 69)％]. Treg cells isolated from the ob/ob mice had stronger immunosuppressive effects on the proliferation of effector T ( Teff) cells and the secretion of TNF-α and IFN-γ than those from the wild-type mice [TNF-α:(1. 6±0. 2)％ vs (2. 4±0. 5)％, IFN-γ:(4. 3±0. 3)％ vs (7. 2±1. 2)％]. The percentages of Treg cells were decreased from (12. 2±1. 8)％ to (7. 6±0. 9)％ upon the in vitro treat-ment of CD4+ T cells from the ob/ob mice with leptin and the immunosuppressive effects of Treg cells were also weakened. However, the percentages of Treg cells were increased from (7. 8±0. 85)％ to (13. 1± 1. 5)％ upon the in vitro treatment of CD4+T cells from the wild-type mice with anti-leptin antibody and the immunosuppressive effects of Treg cells were improved as well. Moreover, the expression of Foxp3, IL-10 and TGF-β at transcriptional level and the levels of IL-10 and TGF-β in the ob/ob group were higher than those in the wild-type group. Conclusions Leptin deficiency significantly promoted the generation of Treg cells in mice and resulted in an increased expression of Foxp3, IL-10 and TGF-βat mRNA level and elevat-ed levels of IL-10 and TGF-β. The treatment of CD4+T cells with leptin might inhibit the generation of Treg cells through down-regulating the transcription of Foxp3, IL-10 and TGF-β.