The effects of Sb on microstructure and mechanical properties of AM50-Y magnesium alloys have been studied. The results show that after Sb is added into the AM50-Y alloy, the grains are refined obviously and a few dispersed?phases YSb are formed, which promote the formation of fine, dispersed?Al2Y particles by providing the nucleation sites. With increasing of Sb content, the tensile strength and elongation at room temperature and at 150 °C, and the impact toughness at room temperature of the alloys increase first, and then decrease. When the content of Sb is up to 0.6%, the tensile strength, elongation and impact toughness at room temperature reach their maxima simultaneously of 257 MPa, 9.9% and 26 J·cm-2, increased by 13.7%, 15.9% and 14.9% respectively compared with the alloy without Sb addition. Meanwhile, the tensile strength and elongation at 150 °C reach their maxima of 203 MPa and 11.9%, increased by 12.8% and 15.5% respectively, showing the best combined mechanical properties