The influence of samarium (Sm) content on the solidification characteristics, microstructure, and mechanical properties of Mg–2.8wt%Nd–1.5wt%Gd–0.5wt%Zn–0.5wt%Zr magnesium alloy was studied. The cooling curves and microstructure analysis results showed that Sm rare earth element refined the grains of the alloys, where the solidification time of α-Mg phase decreased as addition of Sm, which reflected to the microstructure of alloy and the grains became refined, also Sm combined with the initial phase of the intermetallic base alloy and crystallized along the grain boundaries. In addition, Mg₄₁Sm₅, Mg₃Zn₆Sm and (Mg, Zn)₃Sm new intermetallic phases were formed as addition of Sm. Both grain refinement and formed intermetallic phases led to the improvement in hardness and tensile strength.