Objective To assess the effectiveness of a 12‐hour versus 24‐hour intravenous maintenance dose of magnesium sulfate (MgSO4) in women with pre‐eclampsia, and the maternal and fetal outcomes. Methods This was a randomized controlled trial conducted at the labor ward complex of University College Hospital, Ibadan, Nigeria between May and August 2014. Pregnant women with severe pre‐eclampsia were randomized to receive a 12‐hour versus 24‐hour maintenance dose of MgSO4. Study outcomes were occurrence of seizures, adverse maternal effects, neonatal survival, and admission to the intensive care unit. Data analysis involved descriptive statistics and bivariate analysis using Statistical Package for Social Science (SPSS) version 20. Results There were 80 patients randomized to the 12‐hour (n=40) and 24‐hour (n=40) groups. The participants in the two groups had comparable demographic features. There was no significant difference (P>0.999) between the satisfactory maternal outcome following the 12‐hour maintenance dose and the standard 24‐hour regimen (95.0% vs 97.5%). Similarly, there was no significant difference (P=0.276) in perinatal mortality in the 12‐hour versus 24‐hour arm (17.5% vs 12.5%, respectively). No case of eclampsia and maternal death was recorded. Conclusion A 12‐hour maintenance dose of intravenous MgSO4 in the management of severe pre‐eclampsia is effective and safe when compared with the 24‐hour maintenance dose.