Background: Preeclampsia is a hypertensive disorder of pregnancy which is one of the leading causes of maternal and perinatal mortality and pre-term delivery, especially in low and middle income countries. In women with severe PE, the use of magnesium sulfate (MgSO4) is indicated for prevention and control of acute convulsions. Purpose: To determine the effect of the loading dose of magnesium sulfate on the umbilical artery Doppler indices in the patients with severe pre-eclampsia. Patients and Methods: This was prospective observational cohort study, was carried out on 50 patients at Aswan University Hospital. All patients were subjected to detailed history taking and complete physical examination. Results: There was a statistical significant difference between each of the umbilical artery Doppler RI and umbilical artery Doppler PI before and after the administration of loading dose MgSO4 in the studied patients. The decrease in the values of Doppler parameters before and after administration of MgSO4 was observed (p value < 0.001). Conclusion: Doppler flow tests should be included in the sonographic examination. Magnesium sulfate has a vasodilator impact on the blood vessels of the mother and fetus. Several hemodynamic modifications have been observed after using magnesium sulfate. In patients with severe preeclampsia, magnesium sulfate causes major changes in the umbilical artery Doppler indices. In patients with severe preeclampsia, magnesium sulfate should be provided.