Gestational diabetes mellitus (GDM) is an impaired fasting glucose condition during pregnancy. Adiponectin is a polypeptide hormone that is extensively released by adipocytes which regulates energy homeostasis and carbohydrate and lipid metabolism. In addition, adiponectin has antidiabetic and anti-inflammatory properties. The aim of our research was to study about the relationship of adiponectin levels to GDM and glucose intolerance. We selected 25 GDM women and 35 healthy pregnant subjects (18-46 years) who were screened between 24 and 28 weeks of gestation based on the result of oral glucose tolerance test (OGTT). We designed a case-control study and measured the concentrations of serum adiponectin and compared the concentrations between the groups. Serum adiponectin concentration was measured using enzyme-linked immunosorbent assay (ELISA). Sociodemographic data were collected by personal interview. Serum adiponectin concentrations were significantly lower in the subjects with GDM (5.10 ± 2.15 ng/mL vs. 7.86 ± 3.52 ng/mL, p = 0.001) than in healthy pregnant subjects. The mean concentration of fasting blood glucose was considerably lower in control subjects (86.9 ± 9.0 mg/dL vs. 175.9 ± 20.1 mg/dL, p < 0.001) in comparison to GDM subjects. Our findings showed that serum concentrations of adiponectin were significantly lower in gestational diabetic women and this may help to predict the risk of GDM.