The aim of this study is to investigate the levels of 25(OH)D, inflammation markers and glucose and fat metabolism indexes in pregnant women with Gestational diabetes mellitus (GDM).One hundred and ten cases GDM and 100 cases healthy pregnant women in the First People's Hospital of Lianyungang City from October 2016 to December 2018 were recruited for this observational cross-sectional study. Each participant's anthropometric and demographic data was recorded. Blood samples were collected and analyzed to determine the levels of 25(OH)D, high sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-alpha (TNF-α), fasting blood glucose, fasting blood insulin, hemoglobin A1c (HbA1c), homeostasis model assessment of insulin resistance (HOMA-IR), cholesterol and triglycerides.Inflammatory markers and glucose and fat metabolism indexes were all significantly higher in the GDM group than that in the control group, while Serum 25(OH)D level in the GDM group was significantly lower. Serum 25(OH)D levels were negatively correlated with hs-CRP, while not with TNF-α. Furthermore, Serum 25(OH)D, hs-CRP and TNF-α levels were all associated with increased risk of developing GDM.Nowadays, the reports on the association between 25(OH)D level and GDM were controversial. Our results are consistent with the view that there was association between 25(OH)D level and GDM, and expand the literature by showing the roles of 25(OH)D, inflammation markers as well as glucose and fat metabolism indexes in the risk of developing GDM in the pregnant women with the low overall levels of 25(OH)D before delivery. This broadens our knowledge on the pathophysiology of GDM, which may be helpful in prevention and treatment of GDM.