Background: Magnesium sulfate remains the drug of choice for both prevention and treatment of women with eclampsia. Regimens for administration of this drug have evolved over the years, but have not yet been formally evaluated. Objectives: To determine the minimal effective dose of magnesium sulfate in controlling cases of severe preeclampsia and prevention of eclampsia and to determine whether only loading dose of magnesium sulfate is effective in prevention of eclampsia. Material and method :A randomized controlled study that compared three regimens for administration of MgSO4 used for the cases of severe pre-eclampsia that was performed in the Obstetrics & Gynecology Department, Kasr Al-Ainy Hospital, Cairo University during the period from May 2013 to the end of January 2014.The study included 240 pregnant women presenting to the casualty unit with criteria of severe preeclampsia and was divided into three categories:- Category A including 80 patients who took only loading dose of MgSO4 (6 grams of MgSO4 on 250 ml ringer solutions over 20 minutes) with no postpartum maintenance sulfate. Category B including 80 patients given abbreviated doses of MgSO4 (4 grams of MgSO4 on 250 ml ringer solution over 4 hours every 4 hours by IV drip only for 12 hours) in the postpartum period. Category C including 80 patients given full dose of maintenance MgSO4 (4 grams of MgSO4 on 250 ml ringer solution over 4 hours every 4 hours by IV drip for 24 hours) in the postpartum period.Main results: Although strong evidence supports the use of magnesium sulfate for prevention and treatment of eclampsia, 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 24 hours in the studied patients. Conclusion: Considering the equal effectiveness, fewer side effects, ease of monitoring and cost-effectiveness of loading dose, single loading dose of magnesium sulfate in the management of pre-eclampsia is preferable to other regimes of administration requiring multiple doses.