There have been reports on sheet forming of Mg alloy in industry via the punch and die method; this paper is probably the first formal one for studying the sheet formability of AZ31 employing pressurized gas to press the sheet into a female die cavity at various elevated temperatures. The results indicate it is feasible to form a rectangular box via pressurized gas from extruded sheets of 0.5 and 1.7 mm thick. The formed box has 1:2 depth over width ratio, which should be large enough when dealing with realistic industrial sheet forming parts. Presently, forming a sheet of 0.5 mm thick is considered a technical challenge by industry, and it is conquered as demonstrated in this paper. Gas forming technique applied to Mg alloy is unprecedented and shows potential for industrial utilization. There have been reports on sheet forming of Mg alloy in industry via the punch and die method; this paper is probably the first formal one for studying the sheet formability of AZ31 employing pressurized gas to press the sheet into a female die cavity at various The results indicate it is feasible to form a rectangular box via pressurized gas from extruded sheets of 0.5 and 1.7 mm thick. The formed box has 1: 2 depth over width ratio, which should be large enough when dealing with realistic industrial sheet forming parts . Presently, forming a sheet of 0.5 mm thick is considered a technical challenge by industry, and it is conquered as demonstrated in this paper. Gas forming technique applied to Mg alloy is unprecedented and shows potential for industrial utilization.