In Thailand, nebulized ipratropium bromide/fenoterol, is commonly used in addition to salbutamol for severe asthma exacerbation. Recently, nebulized MgSO4 is indicated in GINA 2015 as an additive treatment for severe cases. However, there is limited data showed the efficacy of both drugs in childhood severe asthma. The purpose of this study to compare efficacy and safety of nebulized MgSO4 and ipratropium bromide/fenoterol in moderate to severe asthma attacks.