In this study, melt protection property of SF6+synthetic air and HFC-134a+synthetic air cover gas mixtures were investigated for most commonly used magnesium alloys, AZ91D and AM60B. Each alloy was melted in mild steel crucible with different temperature, cover gas concentrations and sealing conditions. HFC-134a+synthetic air cover gas mixtures offered better melt protection property for all variables of temperatures, alloys, cover gas concentrations and sealing conditions. However, crucible (AISI 1020) surface that is exposed to HFC-134a cover gas mixtures was seriously damaged due to the corrosive characteristics of HFC-134a in molten magnesium temperature.