Introduction: Asthma is a disease with important morbidity and that can lead to death in childhood. The use of intravenous magnesium sulfate has been indicated in cases refractory to the initial management with inhaled bronchodilators and corticosteroids. Objective: To evaluate the use of magnesium sulfate in continuous infusion (50mg/kg/hour in 4 hours) in children with severe acute asthma. Location: 10-bed pediatric emergency room, university hospital. Patients: Children over 2 years old who received a continuous infusion of magnesium sulfate at a dose of 50mg/kg/hour in 4 hours. Methods and main findings: Cross-sectional, prospective study. All patients with severe acute asthma were included in a study protocol. A total of 40 patients met the inclusion criteria, 60% male, with a median age of 3.0 years (2.8-4.3). All patients were monitored and followed by an emergency pediatrician during the 4 hours of infusion. There was no description of adverse events related to the magnesium sulfate. The modified Wood-Downes clinical score was applied and compared before and after the infusion and a significant clinical improvement was observed (p<0.001). The serum magnesium levels at the end of the infusion ranged from 3.3-5.8 mg/dL, suitable as therapeutic and without toxicity (median 4.0). The median length of stay in pediatric emergency was 2 days. Only 2 patients (5%) were transferred to the PICU. Conclusions: On this study, the use of continuous magnesium sulfate proved to be well tolerated, leading to improved respiratory status, and can be considered as adjunctive therapy in the management of severe asthma.