To investigate the effect of Al 8 Mn 4 Gd phase on microstructural and mechanical properties of Mg-Al-Ca magnesium alloy, two Mg-2.5Al 2 Ca and Mg-2.5Al 2 Ca-0.1Al 8 Mn 4 Gd alloys were designed and compared in this work. The results show that a small amount of Gd can significantly refine α-Mg grains and change the morphology of Al 2 Ca particles. Indeed, the formed Al 8 Mn 4 Gd phase could serve as a heterogeneous nucleation site for the α-Mg grains and Al 2 Ca particles. Furthermore, the introduction of Gd not only optimized the mechanical properties of Mg-Al-Ca alloy, but also facilitated the thermal deformation (such as hot rolling).