In this investigation, the fracture and tensile properties of die cast and thixomolded magnesium alloys are compared and shown to be dependent on the microstructure of the test specimens. The principal features of a die cast structure that inhibit crack propagation and contribute to high ductility are the presence of highly structured primary α-magnesium dendrites and a continuous network of the α-magnesium phase. The lower tensile properties of thixomolded magnesium alloys are attributed to the presence of nodular a-magnesium dendrites. Cracks propagate around the nodular dendrites through the divorced eutectic that surrounds the nodular α-magnesium dendrites. In the thixomolded alloys, there is also a less developed continuous network of the α-magnesium phase.