Mg alloys have gained a great attention as light-weight structural materials recently but it could not replace the conventional materials which are being used in automobile and other industries because of high cost of manufacturing processes. Mg alloy must be fabricated under protection gas atmosphere due to high oxidation reaction during melting. This reaction makes a sludge and dross when the melt is not well maintained. The sludge and dross generated during melting is barely removed before cast into the mold. According to our pre-test, the extruded Mg–3Al–1Zn–0.5Mn–1Ca alloy which were treated with N2 gas bubbling process during the melting had higher mechanical properties than alloy which was cast without N2 gas bubbling. However, in our previous work we did not get the optimum conditions for N2 bubbling process. In this study, mechanical properties of extruded Mg–3Al–1Zn–0.5Mn–1Ca alloy, which were fabricated with different melting temperatures and amounts of N2 gas flow was investigated to optimize the variables in N2 bubbling process for melt. The specimen treated and untreated N2 gas bubbling process were extruded by indirect extrusion with billets of diameter of 40 mm after casting. The extrusion temperature and extrusion reduction ratio were 270 °C and 20:1, respectively. In addition, effect of N2 bubbling on microstructure and mechanical properties was also studied.