OBJECTIVE: To investigate the correlation between urinary C-peptide secretion (UCPS) and insulin sensitivity in pregnant women and to provide new ideas for the early detection of gestational diabetes. STUDY DESIGN: We recruited 166 women between 20 and 28 weeks of gestation. Their height and weight were measured to calculate body mass index (BMI). The 75-gram oral glucose tolerance test (OGTT) was carried out to detect serum glucose, serum insulin, and C-peptide levels. The homeostasis model assessment of insulin resistance (HOMA-IR), homeostasis model assessment of β cell function (HOMA-β), the Matsuda index, and serum C-peptide area under the curve (CPauc) were calculated. Additionally, the fasting urine specimen and all urine samples within 2 hours after OGTT were collected to determine the urinary C-peptide and urine volume to calculate UCPS. RESULTS: We found that fasting serum insulin (FINS), fasting serum C-peptide (FCP), BMI, OGTT 2-hour UCPS (UCPS120), CPauc, Matsuda index, and HOMA-IR of the gestational diabetes mellitus (GDM) group were significantly higher than those of the normal glucose tolerance group. FCP was positively correlated with UCPS0 (r=0.234, p=0.002) and HOMA-β (r=0.251, p=0.001). UCPS120 was positively correlated with CPauc (r=0.176, p<0.001), Matsuda index (r=−0.362, p<0.001), and HOMA-IR (r=0.336, p<0.001). The combination of BMI and UCPS120 was better than other indexes in predicting GDM, with a sensitivity of 72.0% and specificity of 70.7%. CONCLUSION: UCPS120 has the potential to be a new index to reflect insulin sensitivity in pregnant women. In screening for GDM, the combination of BMI and UCPS120 was better than other indexes. © Science Printers and Publishers, Inc.