Abstract: Objective：To investigate the correlation between apo B/apo AⅠ ratio and insulin resistance (IR) in patients with polycystic ovary syndrome (PCOS). Methods：Oral glucose tolerance test was carried out on 137 patients with PCOS and 116 healthy women. Serum lipid was simultaneously determined and apo B/apo AⅠ ratio was calculated. Homeostasis model assessment 2-insulin resistance (HOMA2-IR) was completed for all the subjects. Hyperinsulinemic euglycemic clamp was performed in 101 patients with PCOS and 20 healthy women, and the insulin sensitivity was assessed by homeostasis glucose metabolism rate (M value). The subjects were divided into four groups according to the quartiles of M value for the controls and the quartiles of apo B/apo AⅠ ratio for the patients with PCOS. Logistic regression was used to estimate the relationship between the apo B/apo AⅠ ratio and the risk of IR. Results：The level of HOMA2-IR and the apo B/apo AⅠ ratio of the patients with IR were significantly higher than those of the patients without IR, but the reverse was true for M value (P<0.05). The apo B/apo AⅠratio was positively correlated with the levels of body mass index (BMI), fasting plasma glucose (FPG), 2hour post-load plasma glucose (2h-PPG), fasting serum insulin (FINS) and HOMA2-IR, but negatively with M value (P<0.05) in the patients with PCOS. The risk producing IR in the group with the highest quartile of the apo B/apo AⅠratio was 5.42 times higher than that with the lowest quartile of the apo B/apo AⅠratio (P<0.05). Conclusion：The apo B/apo AⅠratio is closely related to the development of IR in the patients with PCOS, and high apo B/apo AⅠratio is a potential biomarker for predicting the development of IR.