Abstract: The effect of mixed addition of Ce,Sr and Ba elements on microstructure and mechanical properties of the AZ91 magnesium alloy by means of optical microscope,X-ray diffraction analyzer,scanning electron microscope and energy dispersive spectroscopy was investigated.The results show that the as-cast microstructure as well as room temperature mechanical properties could be greatly refined and improved by mixed addition of Ce,Sr and Ba.In the case of simultaneous addition of 0.5wt%Ce,0.2wt%Sr and 0.2wt%Ba,the grain-refining effect of the alloy was the best,the grain size was the smallest,and the quantity of the small bulk β-Mg17Al12 phase which distributed dispersively in the matrix was the most.The tensile strength as well as the elongation of the alloy increased by 25.0% and 24.0% than the alloy without alloy element addition,up to 195 MPa and 1.86% respectively.