The effects of antimony (Sb) and strontium (Sr) additions on the microstructure of Mg-Al-Si alloys were studied. The results show that the additions of Sb and Sr can modify the Mg2Si particles from Chinese script shape to refined polygonal shape. Tensile strength and creep resistance are improved, and tensile elongation is also increased in the modified alloy. Sr modification is more effective than Sb modification of AS52 alloy for refining the microstructure and thus improving its properties.