Several Mg alloys were processed to achieve the thixotropic microstructure of non-dendritic, globular primary grains for semisolid forming using a novel method that does not require stirring. The alloys were poured at their liquidus temperatures or about ten degrees below the liquidus temperatures using either batch or semi-continuous casting. Although the compositions of the alloys had considerable effects on details of the resulting microstructure, generally fine, equiaxed primary grains were obtained by controlling the resting time, casting speed and cooling rate. The lower casting temperatures and addition of calcium were effective in preventing burning of Mg without using a protective atmosphere. This new method has great potential for industry applications.