Introduction: Preeclampsia is a common and serious hypertensive disorder affecting approximately 5-8 % of pregnancies. The biology of the disease is complex and not understood. This disease associated with increased blood pressure more than 140/90 mmHg in the second half of pregnancy and proteinuria more than 300 mg/24 h and is considered as one of the three leading causes of maternal and fetal mortality and related complications. This complication is a systemic disorder and can lead to difficulties in the mother, such as kidney and liver dysfunction. As well as, the risk of injury in the fetus, such as fetal growth restriction, which is considered as one of the most important causes of neonatal mortality, is common. Various factors are involved in the onset of this disease including vascular activating proteins, oxidative stress, endothelial damage and other cases (1-5). Oxidative stress is an imbalance between the production of ROS and antioxidant defences, resulting in increased levels of ROS with resultant damage of cellular components including DNA, proteins and lipids. Normal pregnancy is characterised by a low grade oxidative stress; there are increased circulating levels of oxidised low-density lipoproteins and a reduction in total antioxidant capacity in pregnant women when compared with non-pregnant women. Excessive oxidative stress is generally thought to be involved in the pathology of many pregnancy-related disorders such as fetal growth restriction (FGR), preeclampsia and miscarriage. Dysfunctional placentation is proposed to provoke a hypoxic reperfusion injury causing elevated oxidative stress in preeclampsia. By 10– 12 weeks’ gestation in normal pregnancy maternal blood flow in the placenta causes a local increase in oxygen and elevation in the activity of the antioxidant enzymes. One of the most relevant enzymatic antioxidants is glutathione peroxidase (GPx). Currently there is no treatment for preeclampsia except delivery of the placenta and the baby, with the attendant risk of iatrogenic prematurity and significant neonatal morbidity and mortality. As a result, intensive research endeavours have focused on defining the molecular mechanisms of preeclampsia and the identification of new pre symptomatic biomarkers of the condition (6-11). It seems that the polymorphisms in the Glutathione peroxidase1 gene is one of the leading causes of the disease (13, 14). This study aimed of this study was to evaluate the relationship between Glutathione peroxidase1 gene (GPX1pro198Leu) polymorphism with preeclampsia. Materials and method: In the present case-control study conducted at Islamic Azad University of Kazerun in 2017, 150 preeclampsia patients with systolic blood pressure ≥ 140 mm Hg or diastolic blood pressure ≥ 90 mm Hg with two repetitions and at least 6 hours apart and also Proteinuria /0 0. 3 g in 24-hour urine with ≥ +1 were in urine strip test were selected from patients referred to Vali-e-Asr Hospital in Kazerun for further molecular studies. In order to select women in the case group, first all diagnosed with preeclampsia were selected as candidates for the study, and after reviewing the clinical history, women with a history of any internal diseases were excluded from the study. The women in the control group (150 women) were selected from healthy pregnant women who had referred to the hospital for routine examinations and were matched to the patient group in terms of gestational age and place of residence. 5 ml of peripheral blood was collected from the subjects. Then DNA was extracted by salting out method. Polymorphism was determined using PCR-RFLP method. Data were analyzed using SPSS software and Chi-square statistical tests. Results: Results showed that the products of each genotype appeared on the gel as bands of 261 and 75 bp for CC homozygotes, 336, 261 and 75 bp for CT heterozygotes and 336 bp for TT homozygotes. The results of chi-square test showed a significant relationship between the control group and the patient in the frequency of CC, CT and TT genotypes in the GPx1Pro 198Leu polymorphism position (PGPX1 = 0. 047). There was no significant relationship between the control group and the patient in the frequency of both C and T alleles in the Gpx1Pro198Leu polymorphic position (PGPX1 = 0. 671). The results of the study of the relationship between Gpx1Pro 198Leu polymorphism and paraclinical factors, including; Severity of preeclampsia, urinary protein excretion, patient swelling, age at onset of disease, primi para, multiple pregnancy, previous history of preeclampsia, history of miscarriage, diabetes mellitus and hypothyroidism showed that except for the multipara parameter (PGPX1 = 0. 018) Significant relationship between other parameters studied such as Severity of preeclampsia (PGPX1 = 0. 209), urinary protein excretion (PGPX1 = 0. 710), patient swelling (PGPX1 = 0. 419), age at onset of disease (PGPX1 = 0/069), primipara (PGPX1 = 0/160), previous history of Preeclampsia (PGPX1 = 0/539), history of miscarriage (PGPX1 = 0/708), diabetes mellitus (PGPX1 = 0 / 110) and hypothyroidism (PGPX1 = 0. 221) with the mentioned polymorphism was not seen in the patient and control groups. Conclusion: Due to serious risks of preeclampsia to mothers and infants, identifying markers that can predict the risk of this outcome is importance. Researchers have linked the gene polymorphisms to individual disease susceptibility and response to drug, and suggest that their presence may be a predictor of disease risk. In the present study, the relationship between Glutathione peroxidase1 gene (GPX1pro198Leu) polymorphism with preeclampsia was investigated. This polymorphism, by replacing cytosine with thymine at nucleotide 599 (C. 599C> T) of exon 2 of the GPX1 gene, converts the amino acid proline to leucine and affects enzyme activity. The results showed that the frequency of CC, CT and TT genotypes, despite the frequency of C and T alleles in the Gpx1Pro198Leu polymorphism site, the gene encoding glutathione peroxidase 1 among pregnant women with preeclampsia and Healthy pregnant women have a significant difference. In 2012, a polymorphism (rs713041) related to the gene encoding the enzyme glutathione peroxidase 4 with preeclampsia was also demonstrated. Similarly, in this study, the existence of a significant difference in the percentage of homozygous individuals for the C allele in the polymorphic position indicates the association of polymorphism with the incidence of the disease (19). There are also other studies linking the T allele of the Gpx1Pro198Leu polymorphic site to the occurrence of some diseases such as They have proven lung malignancy (20), cerebral hemorrhage (21) and coronary artery disease (22). Also, in a recent study conducted in 2018, the presence of CAT-21A / T polymorphism in the catalase-encoding gene has been introduced as a predisposing factor for preeclampsia (23). In this study, the association of Gpx1Pro198Leu polymorphism with factors such as; Severity of preeclampsia, urinary protein excretion, patient swelling, age at onset of disease, primi para, multiple pregnancy, previous history of preeclampsia, history of miscarriage, diabetes mellitus and hypothyroidism Checked out. In other cases except for the multiplicity parameter, no significant relationship was observed with Gpx1Pro198Leu polymorphism. However, since the occurrence of preeclampsia is most likely the result of the interaction of several polymorphic genes (24), the absence of a significant association between a gene polymorphism and disease risk factors will not be unexpected, so it is better to achieve a more reliable assessment of polymorphism status in different genes should be examined. Considering the significant relationship between Gpx1Pro198Leu polymorphism and the occurrence of preeclampsia, which emphasizes the role of genetic predisposition in the occurrence of this disease, the presence of this polymorphism can be predicted as a factor Considered the cause of preeclampsia.