Background: Preeclampsia is serious syndrome that can affect human pregnancy causing serious complications. Preeclampsia is pregnancy-specific syndrome of reduced organ perfusion secondary to vasospasm and endothelial activation. Objective: The aim of our study was to assess the comparative effects of three regimens for the administration of the magnesium sulfate when used for the care of women with severe preeclampsia to determine the effective dose of magnesium sulfate in controlling cases with severe preeclampsia and prevention of eclampsia and to determine whether only loading dose of magnesium sulfate is effective in prevention of eclampsia or not. Patients and methods: The study included 240 pregnant women presenting to the casualty unit diagnosed as cases of severe preeclampsia in the Obstetrics and Gynecology Department, Al-Azhar University Hospital and EL Mahalla General Hospital. A randomized controlled study that compared three regimens for administration of MgSO4 used for these cases. Results: There was no significant difference between occurrence of eclampsia in the three groups after either administration of loading dose of MgSO4 only or administration of loading dose with maintenance dose for 12 hours or maintenance dose for 24 hours in the studied patients. Conclusion: Magnesium sulfate proved to cause many hemodynamic changes as it has vasodilator effect on maternal and fetal blood vessels. Magnesium sulfate should be given to all patients with severe preeclampsia.