Purpose of investigation: In this study we aimed to measure the activity of catalase, which is an antioxidant enzyme, the concentrations of some trace elements and heavy metals, and vitamin A, D and E levels in serum samples of patients with hydatidiform mole, normal pregnancies and healthy non pregnant women. Methods: Seventy-two women were enrolled in this study. Of these, 24 were healthy women in the first trimester of pregnancy (HP), 24 were healthy non-pregnant women (NP) and 24 were patients with complete hydatidiform mole (CHM). Results: Serum levels of catalase, Zn, Co, vitamin A, D and E were significantly lower in the CHM group when compared with the HP and NP groups (p < 0.001). Serum levels of Cu, Fe, and Cd were significantly higher in the CHM group when compared with the HP and NP groups (p < 0.001). Conclusion: The assessment of oxidant/antioxidant imbalance in pregnant women could be useful in the early determination of molar pregnancy and supplementation with antioxidants may be useful in the treatment of CHM, and may prevent recurrent molar pregnancy.