Objective：To investigate the clinical features of patients with polycystic ovary syndrome（PCOS） and autoimmune thyroiditis（AIT）. Methods：The clinical data of 51 patients with PCOS were collected，including age，body mass index，thyroid function，thyroid autoimmune antibodies，biochemical parameters，hormone levels，and ovarian morphology on ultrasound，and a statistical analysis was performed. Results：The PCOS patients with positive thyroid autoimmune antibodies had significantly higher serum estradiol level and estradiol-to-progesterone ratio than those with negative thyroid autoimmune antibodies [serum estradiol level：193（144-251） vs. 148 （94.8-193.25），P <0.05；estradiol-to-progesterone ratio：155.17（69.17-319.72） vs. 112.91（79.18-141.55），P <0.05]. Compared with those with polycystic ovaries，the PCOS patients without such manifestation had significant increases in serum estradiol level[201 （149-350） vs. 174 （105.3-196），P <0.05]，estradiol-to-progesterone ratio[209.38（105.19-341.11） vs. 116.86 （83.74-153.75），P <0.05]，and positive rate of thyroid autoimmune antibodies（P <0.05）. In the PCOS patients，the serum level of thyroid autoimmune an－tibodies was positively correlated with serum estradiol level and estradiol-to-progesterone ratio（P <0.05）. Conclusion：The PCOS pa－tients without polycystic ovaries tend to develop AIT. The pro－duction of thyroid autoimmune antibodies may be associated with the increases in serum estradiol level and estradiol-to-pro－gesterone ratio.