This study has investigated the effect of aging treatment on the microstructure and mechanical properties of Mg-6Al-xZn(x = 1.5, 2.5) alloys fabricated by the squeeze casting process. The microstructures of as-squeeze cast were composed of pro-eutectic ${alpha}$, super saturated ${alpha}$ and ${eta}(Mg_{17}Al_{12})$ compound. Aged at both $200^{circ}C$ and $240^{circ}C$, Mg-6Al-xZn alloys showed the peak hardness due to the formation of ${eta}(Mg_{17}Al_{12})$ precipitates. The discontinuous precipitates of the lamella type are predominant at $200^{circ}C$ aging treatment, while the finely dispersed continuous precipitates were dominant at $240^{circ}C$ aging treatment. Mg-6Al-xZn alloys fabricated by the squeeze casting process had the better combination of tensile strength and elongation compared to the conventionally cast alloys. As zinc contents increased, the tensile strength was increased by the solid solution strengthening effect of zinc.