Objectives: Investigation of the association of serum iron and ferritin with insulin resistance (IR) indices in pregnant women with gestational diabetes mellitus (GDM). Methods: Serum ferritin and iron and IR indices were measured in the 50 pregnant women with GDM and 350 non-GDM, and association of IR indices with serum iron and ferritin was evaluated. Results: Ferritin in the GDM group was significantly correlated with all IR indices except HOMA-B. No significant relationship found between iron levels and IR indices, except HOMA-IR. Conclusion: Increased serum iron and ferritin levels may increase insulin resistance and the risk of developing GDM.