In accordance with the ignition-prevention mechanism of F-containing shielding gas, HFC125 (pentafluoroethane) possesses the potential for forming a F-containing dense film on the surface of a Mg melt to protect it from oxidation and ignition. Importantly, HFC125 has a GWP (global warming potential) value around one eighth that of SF6, and is one-third the price (in China). The effect of HFC125, diluted in a nitrogen based shielding gas was examined via systematic experiments under variable temperature, concentration, and flux. The results showed that a shiny metallic film instantly formed on the surface of an Mg melt similar to what was observed with SF6. The protective effect varied with temperature, concentration and flux. The chemistry and structure of the protective film was characterized by SEM, EDS and XRD, and showed that the film was a dense, continuous layer of Mg oxide and fluoride. The results obtained lead to a conclusion that HFC125 is capable of providing effective protection and is, therefore, an ideal alternative to SF6 in terms of protective effectiveness, reduced GWP and cost.