Background: Gestational Diabetes has been increasing recently. This condition, which can cause extremely negative results for the mother and baby, can be taken under control by removing the lack of information. Objectives: This study aimed to examine the knowledge levels of pregnant women concerning Gestational Diabetes Mellitus (GDM), and to determine the factors that affect the knowledge levels. Methods: This research was conducted as a descriptive cross-sectional study. The sample was comprised of 184 pregnant women. The research data were evaluated by the multiple regression analysis. Results: The mean score of GDM knowledge level of pregnant women is 40.10 ± 19.56 (min = 0, max = 88) points. Monthly mean income (β = .185, t = 2.779, p = .006), treatment method (β = .318, t = 3.422, p = .001), status of receiving education (β = .267, t = 4530, p = .000), pregnant women evaluated GDM knowledge which level (β = -.348, t = 6.008, p = .000), and person who gave the education (β = .180, t = 3.375, p = .001) were determined to be predictors of Gestational Diabetes Mellitus knowledge (R2 = .66, F = 25.690, p = .000). Conclusion: Having high income, receiving insulin treatment beside the diet, receiving education about GDM, thinking they have information about GDM, and multidisciplinary approach were found the factors affecting GDM knowledge.