With the aim to further improve the mechanical properties of Mg-A1-RE-based alloy, Mg-3.0Al-1.8Ce-0.3Y-0.2Mn alloy was prepared by high-pressure die-casting technique. The microstructure, thermal stability of intermetallic phases and mechanical properties were investigated. The results show that the alloy is composed of fine primary a-Mg dendrites and eutectic in the interdendritic regions. The intermetallic phases in eutectic are Aln（Ce,Y）3 and A12（Ce,Y） with the former being the dominant one. The thermal stability of Al11（ce,Y）3 is conditioned. It is basically stable at temperature up to 200℃ within 800 h, while most of the Al11（Ce,Y）3 intermetallics transform to A12（Ce,Y） at higher temperature of 450 ℃ for 800 h. The alloy exhibits remarkably improved strength both at room temperature and 200℃, which is mainly attributed to the reinforcement of dendrite boundaries with Alll（Ce,Y）3 intermetallics, small dendritic arm spacing effect as well as the solid solution strengthening with Y element.
