Objective To investigate the influence of Leptin on the proliferation of peripheral blood regulatory T cells in patients with rheumatoid arthritis (RA).Methods Peripheral blood mononuclear cells (PBMCs) were isolated from 6 RA patients.RA PBMCs were stimulated with anti-CD3 (3 μg/ml)/anti-CD28(2 μg/ml) antibody for 72 h,anti-CD3 (3 μg/ml)/anti-CD28 (2 μg/ml) antibody and Leptin (100 ng/ml) for 72 h,anti-CD3 (3 μg/ml)/anti-CD28 (2 μg/ml) antibody and Leptin (100 ng/ml) and interleukin (IL)-6 receptor antagonist (0.5 μg/ml) for 72 h.Regulatory T cells (Treg) were detected by flow cetometry.IL-6 level and TGF-βlevels in the supernatants of RA PBMCs culture were detected by Enzyme linked immunosorbent assay(ELISA).Statistical analysis between the two groups were performed by Wilcoxon Signed Rank Test.Results ①) Our results suggested that compared to the control group,RA PBMCs were stimulated by leptin for 72 h had lower percentage of Treg[13.6(11.6,14.8)％ vs 9.8(7.0,10.0)％,Z=-2.201,P＜0.05];Compared to the control group,the level of IL-6 and TGF-β were elevated when RA PBMCs treated with leptin for 72 h [548.9(508.6,608.4)ng/L vs 631.8(538.4,672.6) ng/L,Z=-1.992,P＜0.05;1175.0(1 045.4,1 373.1) ng/L vs 1 580.2(1 315.3,1 906.5) ng/L,Z=-2.201,P＜0.05];② The percentage of Peripheral Treg was increased [9.8(7.0,10.0)％ vs 12.3(9.7,13.8)％,Z=-1.997,P＜0.05] and the level of IL-6 was decreased [631.8(538.4,672.6) ng/L vs 522.7(339.3,593.3) ng/L,Z=-2.201,P＜0.05] when RA PBMCs was stimulated with IL-6 receptor antagonist and anti-CD3/anti-CD28 antibody and Leptin for 72 h.Conclusion The study has shown that Leptin can down-regulate the percentage of RA peripheral blood Treg via increasing IL-6 secretion.