Objective  To investigate the regulating effect of adiponectin on the balance of Th17/regulatory T cells (Treg) in peripheral blood of patients with unexplained recurrent spontaneous abortion (URSA). Methods  URSA patients were selected as subjects and healthy nonpregnancy and normal pregnancy women were selected as controls. Serum and peripheral blood mononuclear cells (PBMCs) were isolated. The levels of serum adiponectin, interleukin 17 (IL-17), and transforming growth factor-β (TGF-β) were detected by ELISA. The populations of Th17/Treg cells were observed by flow cytometry. PBMCs of URSA patients were treated by adiponectin of different concentrations in vitro and the levels of IL-17 and TGF-β in supernatant were detected by ELISA, the change of populations of Th17/Treg cells was observed by flow cytometry, and the mRNA expressions of transcription factors RORγt and FOXP3 were detected by real-time PCR. Results  Serum adiponectin levels of URSA patients significantly decreased and the imbalance of Th17/Treg was found. Adiponectin treatment increased the ratio of Treg cells, decreased the ratio of Th17, increased TGF-β level in culture supernatant, decreased IL-17 level, up-regulated mRNA expression of FOXP3, and down-regulated mRNA expression of RORγt. These effects were all dose-dependent. Conclusion  Deficiency of adiponectin and imbalance of Th17/Treg exist in patients with URSA. Adiponectin treatment in vitro can dose-dependently ameliorate the imbalance of Th17/Treg in PBMC of patients with URSA, suggesting that adiponectin may protect the pregnancy by regulating the balance of Th17/Treg.