Objective：To investigate circulating betatrophin levels in females with polycystic ovary syndrome（PCOS） and its correla－tion with insulin resistance（IR）. Methods：Forty-four women with PCOS and thirty-five healthy women were recruited in a cross-sec－tional study. Serum concentrations of betatrophin was measured by enzyme-linked immunosorbent assay（ELISA）. The correlation of betatrophin with IR and metabolic parameters was also analyzed. Then twenty-seven PCOS patients were studied longitudinally after three mouths of metformin and rosiglitazone sodium treatment. Results：Serum betatrophin levels were lower in PCOS patients than in healthy control subjects（0.43±0.15） ng/mL vs. （1.17±0.57） ng/mL，P=0.000. Serum betatrophin negatively correlated with fasting plasma glucose（FPG），2h postprandial plasma glucose（2hPG），fasting insulin（FINS），homeostatic model assessment insulin resistance（HOMA-IR），high-sensitivity C-reactive protein （hs-CRP），even after controlling for age and body mass index（BMI） in PCOS par－ticipants（r=-0.331，r=-0.372，r=-0.311，r=-0.337，r=-0.338，all P<0.05）. Moreover，stepwise multiple regression analysis showed that HOMA-IR was independently related to betatrophin in PCOS subjects（P<0.05）. After rosiglitazone sodium and metformin treatment，PCOS patients showed higher betatrophin concentrations than its baseline levels（0.87±0.51） ng/mL vs. （0.42±0.17） ng/mL，P=0.000. Conclusion：Circulating betatrophin levels are de－creased in patients with PCOS，and associated with IR.