The aim of this study was to examine the relationship between insulin sensitivity and polychlorinated biphenyls (PCBs) exposure in non-diabetic pregnant women. Forty gravidas, 21-39 years of age and residing within the study area, were recruited. Seventeen 2,3,7,8-substituted dichloro-p-dioxin, dibenzofurans and 12 PCBs were measured using high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). Serum insulin and glucose were also measured. Insulin sensitivity and the quantitative insulin sensitivity check index (QUICKI) were calculated based on fasting glucose and insulin levels. Three specific congeners of PCBs (123, 126, and 169) were significantly associated with insulin activity (r=-0.34 approximately -0.36, p<0.05). Statistical analyses revealed that insulin sensitivity was significantly associated with age- and pre-pregnancy body mass indices (BMI)-adjusted for decreasing toxic equivalents (TEQ) of PCBs (p=0.02 for age- and BMI-adjusted). We also performed an insulin correlation for total TEQ and the TEQ of PCBs, and determined that insulin sensitivity was predicted by the TEQ of PCBs by a regression coefficient of -0.189 after adjustment for age and pre-pregnancy BMI. These findings suggest that PCBs may be associated with decreasing insulin sensitivity in non-diabetic pregnant women; however, the mechanism remains to be ascertained.