Objectives: The purpose of this study was to evaluate serum G protein-coupled estrogen receptor-1 (GPER1) levels in non-pregnant and pregnant with and without gestational diabetes mellitus (GDM).,Methods: The study comprised 40 pregnant women with (n=20) and without GDM (n=20) and 20 healthy non-pregnant women. Data as maternal age, gestational age, and body mass index (BMI) of participants were recorded and serum samples were collected. Serum GPER1 levels were measured by enzyme-linked immunosorbent assays.,Results: Serum GPER1 level was significantly higher in GDM (p=0.03) and non-pregnant women (p=0.005) than those of normal pregnancy. There was no significant correlation between the serum GPER1 levels age (r=0.18, p=0.34), gestational age (r=-0.22, p=0.47), and BMI (r= 0. 0 04, p= 0.975).,Conclusions: Our results suggest that changes in serum GPER1 levels in pregnancy and GDM may be associated with estrogen. More detailed studies should be conducted to monitor the changes and their interactions in serum sex hormones and serum GPER1 levels during GDM.