Objectives: The aim of this study was to investigate the influence of body mass index (BMI) on clinical and metabolic characteristics in patients with polycystic ovary syndrome (PCOS). Methods: A total of 67 patients with PCOS were included in this study. Study subjects were divided into two groups according to BMI: women with BMI ≥23 ㎏/㎡(overweight/obese group, n=24) vs. women with BMI <23 ㎏/㎡ (normal-weight group, n=43). We compared clinical and metabolic characteristics including waist-to-hip ratio, serum lipid profiles, homeostatic model assessment of insulin resistance (HOMA-IR), fasting serum glucose/insulin ratio, postprandial 2 hours (PP2) serum insulin levels, total testosterone, sex hormone-binding globulin (SHBG), high-sensitivity C-reactive protein (hs-CRP) and homocysteine levels between the two groups, which were statistically analyzed using Mann-Whitney U test or Fisher’s exact test, where appropriate. Results: The overweight/obese group has a lower serum SHBG level (37.23±26.74 vs. 66.42±40.16 nmol/l, P= 0.004) and a higher free androgen index (5.83±3.85 vs. 3.57±2.30, P=0.002) than the normal-weight group. Fasting insulin (17.13±8.8 vs. 7.15±4.41 μIU/ml, P<0.001), PP2 insulin (76.81±43.66 vs. 47.98±49.77 uIU/ml, P=0.022) and the HOMA-IR (3.65±1.74 vs. 1.48±1.02, P<0.001) are significantly higher and fasting glucose/insulin ratio (6.59±4.84 vs. 15.18±7.48, P<0.001) are significantly lower in the overweight/obese group compared to those of the normal weight group. Serum triglyceride (125.00±105.34 vs. 77.56±41.69 mg/dl, P=0.036) and hs-CRP levels (3.53±4.23 vs. 0.85±0.70 mg/l, P=0.008) are significantly higher in the overweight/obese group. Conclusion: The overweight and obese women with PCOS are more closely related to hyperandrogenism, insulin resistance and chronic inflammation. These findings may indicate that they have an increased risk of metabolic and cardiovascular diseases