BACKGROUND@#Gestational diabetes mellitus (GDM) is a common complication during pregnancy. Obesity and overweight are closely related to metabolic diseases and diabetes. However, the role of adipose tissue in the pathogenesis of GDM remains to be studied. The aim of this study was to investigate the correlation of vitamin D (VD) levels, VD receptor (VDR), and peroxisome proliferator-activated receptor γ (PPARγ) expression with GDM in overweight or obese women.@*METHODS@#One hundred and forty pregnant women with full-term single-birth cesarean-section were selected as the study subjects and grouped (70 GDM women, including 35 non-overweight/non-obese women [group G1] and 35 women with overweight or obesity [group G2]; 70 pregnant women with normal glucose tolerance, including 35 non-overweight/non-obese women [group N1] and 35 overweight/obese women [group N2]). The levels of serum VD, blood biochemistry, and adiponectin were compared in these women. Subcutaneous adipose tissue was isolated from the abdominal wall incision. VDR and PPARγ messenger RNA (mRNA) transcript levels in these adipose tissues were quantified by real-time polymerase chain reaction. The differences between the levels of PPARγ protein and phosphorylated PPARγ Ser273 were detected by Western blotting.@*RESULTS@#The serum VD level of GDM women was lower in comparison to that of women with normal glucose tolerance (G1 vs. N1: 20.62 ± 7.87 ng/mL vs. 25.85 ± 7.29 ng/mL, G2 vs. N2: 17.06 ± 6.74 ng/mL vs. 21.62 ± 7.18 ng/mL, P < 0.05), and the lowest in overweight/obese GDM women. VDR and PPARγ mRNA expression was higher in the adipose tissues of GDM women in comparison to that of women with normal glucose tolerance (VDR mRNA: G1 vs. N1: 210.00 [90.58-311.46] vs. 89.34 [63.74-159.92], G2 vs. N2: 298.67 [170.84-451.25] vs. 198.28 [119.46-261.23], PPARγ mRNA: G1 vs. N1: 100.72 [88.61-123.87] vs. 87.52 [66.37-100.04], G2 vs. N2: 117.33 [100.08-149.00] vs. 89.90 [76.95-109.09], P < 0.05), and their expression was the highest in GDM + overweight/obese women. VDR mRNA levels positively correlated with the pre-pregnancy body mass index (BMI), pre-delivery BMI, fasting blood glucose (FBG), homeostasis model assessment of insulin resistance (HOMA-IR), and PPARγ mRNA while it negatively correlated with the VD and the adiponectin levels (r = 0.395, 0.336, 0.240, 0.190, 0.235, -0.350, -0.294, respectively, P < 0.05). The degree of PPARγ Ser273 phosphorylation increased in obese and GDM pregnant women. PPARγ mRNA levels positively correlated with pre-pregnancy BMI, pre-delivery BMI, FBG, HOMA-IR, serum total cholesterol, triglyceride, free fatty acid, and VDR mRNA, while it negatively correlated with the VD and adiponectin levels (r = 0.276, 0.199, 0.210, 0.230, 0.182, 0.214, 0.270, 0.235, -0.232, -0.199, respectively, P < 0.05).@*CONCLUSIONS@#Both GDM and overweight/obese women had decreased serum VD levels and up-regulated VDR and PPARγ mRNA expression in adipose tissue, which was further higher in the overweight or obese women with GDM. VD may regulate the formation and differentiation of adipocytes through the VDR and PPARγ pathways and participate in the occurrence of GDM.