The effect of Cerium addition to Mg-5Sn alloy and its influence on the microstructure and mechanical properties of the alloy were investigated in this work. The microstructural investigations indicate that the alloying addition of Ce leads to effective grain refinement. Also, it was observed that adding Ce to the Mg-5Sn alloy results in the formation of new phases in the alloy such as Ce5Sn4 and CeMgSn. These intermetallic phases were considered to be effective on the enhancement of the hardness of Mg-5Sn alloy. Furthermore, the tensile test results at room temperature and elevated temperatures revealed that the yield and tensile strength of the Ce added alloy were higher than those of the base alloy. The elongation was also improved up to 5 wt% Ce addition while higher amounts decreased the elongation both at room and elevated temperatures.