Purpose: The C-reactive protein/albumin ratio (CAR) has been reported as a novel inflammatory marker to assess inflammation. The aim of this study was to compare the levels of CAR as a inflammatory marker in gestational diabetes mellitus (GDM) and non GDM patients. Materials and Methods: Eight hundred ten pregnant women who applied to our hospital for routine antenatal screening were included in this prospective case-control study. The patients were divided into two groups, as positive and negative diagnosis of GDM. CAR between groups was compared as the primary outcome using statistical methods. Results: The CAR value was significantly higher in pregnancies with GDM compared to healthy controls [1.07 (0.43–1.89) vs. 0.37 (0.12–0.68), p<0.0001]. The Spearman’s correlation analysis revealed that the CAR value had a significant positive correlation with all three steps of 75 gr oral glucose tolerance test (p<0.0001 for each) and neutrophil to lymphocyte ratio value (p=0.011). Conclusion Considering that laboratory testing is very simple and inexpensive, CAR is an independent predictor that is clinically easy to use for the development of GDM. This report is the first to show the role of CAR in GDM. However, further studies with larger sample sizes are needed to generalize this comment.