Gestational diabetes mellitus (GDM) is a common complication during pregnancy and one of the main causes of adverse fetal-maternal outcomes. However, the pathogenesis of GDM has not been clearly stated. Adiponectin, an adipose tissue-derived plasma protein, is involved in regulation of insulin resistance and glucose hemostasis, and thus is a key modulator of insulin action and glucose metabolism. In this study, we investigated to compare serum adiponectin levels in pregnant women with diabetes, pregnant women who are without diabetes, and non-pregnant women, and to evaluate relationship between serum adiponectin. levels and metabolic parameters. Forty-one pregnant women with diabetes, fifty-nine pregnant women without diabetes and forty non-pregnancy women were recruited. Adiponectin levels were significantly lower in pregnant women with diabetes when compared to non-pregnant women and pregnant women without diabetes. Pregnant women without diabetes at second trimester had lower adiponectin levels compared to non-pregnant women. Adiponectin was negatively correlated with BMI, fasting insulin, HOMA-IR, total cholesterol, and triglyceride. In conclusion, this study confirmed that the decreased level of adiponectin precedes the onset of abnormal glucose level during pregnancy and also normal pregnant women had lower adiponectin levels compared to non-pregnant women. This knowledge may help to identify strategies for lowering the occurrence of GDM in women who are at high risk of developing the disorder.