Objective: To determine the effects of routine iron supplementation on oxidative stress markers in pregnant women. Methods: This study enrolled 122 pregnant women aged between 20-38 years throughout three stages of pregnancy: beginning with pregnancy, until the twentieth week and up to the thirtieth week. They were divided into two groups: 61 pregnant women not supplemented with iron (the control group), and 61 pregnant women supplemented with iron (the iron group). Blood samples were collected and protein, iron, uric acid, total bilirubin level and oxidative stress status were estimated using molecular spectrophotometric method. Copper levels were estimated by using atomic absorption spectroscopy method. Results: Iron, protein and copper concentrations were significantly increased (P＜0.05) at 20 and 30 weeks of pregnancy and hemoglobin level was significantly increased (P＜0.05) at the beginning of pregnancy and until 20 weeks in the iron group compared to the control group. In addition, levels of serum uric acid, serum total bilirubin and malondialdehyde in serum and erythrocytes were significantly increased at 20 and 30 weeks of pregnancy whereas the reduced glutathione level was significantly decreased in serum (30 weeks of pregnancy) and erythrocytes (20 and 30 weeks of pregnancy) in the iron group as compared to the control group. Serum oxygen radical absorbance capacity was not significantly changed. There was a significant positive correlation between serum iron level and serum copper, malondialdehyde level in serum and erythrocytes in pregnant women supplemented with iron. Conclusions: Iron supplement at 20 and 30 weeks of pregnancy plays a role in the development of oxidative stress which is the origin of several matal-fetal complications.