Objective: To evaluate the use of aerosolized magnesium sulfate (MgSO4) in combination with inhaled betaagonists compared to inhaled beta-agonists alone in the treatment of acute asthma. Methods: Published (1966-2005) randomized controlled trials were retrieved using different databases, bibliographic reviews of primary research, review articles, and citations from texts. The primary outcome measure was pulmonary function. Results: Five out of 16 potentially eligible studies met criteria for inclusion in the meta-analysis. They included 187 adults and 62 children who were treated in an emergency department. Patients that received MgSO4 showed non-significant improvement in pulmonary function (SMD = -0.21, 95%CI:-0.52 to 0.10, p = 0.18). The advantage of the use of MgSO4 was demonstrated only in patients with life-threatening acute asthma (baseline FEV1 or PEF < 30% predicted) (SMD = - 1.10; 95%CI: -1.80 to -0.39, p = 0.002; I2 = 0%). Nebulized MgSO4 with beta-agonists showed a marginal significant reduction in admission rate compared to beta-agonists alone (RR = 0.63, 95% CI: 0.39 to 1.01, p = 0.06, I2 = 0%). Conclusions: Data suggests that MgSO4 presents a beneficial effect in terms of pulmonary function only in the subgroup of life-threatening acute asthma patients. However, the small number of studies selected, the standard treatment used in all trials, and the beta-agonist delivery method restricts this conclusion.