Abstract: The microstructure and corrosion resistance of as-cast Mg-4Al-3Ca-0.7Mn-xY (x=0, 0.8, 1.5) alloys were investigated by metallographic microscope, scanning electron microscope, XRD, corrosion test and electrochemical test.The results show that the microstructure of Mg-4Al-3Ca-0.7Mn alloy without Y is composed of α-Mg, Al₂Ca and Mg₂Ca phases.After adding 0.8wt%Y, the grains in the microstructure of the alloy are obviously refined, and the precipitation phase is fine.The number of Al₂Ca and Mg₂Ca phases is reduced, and the Al₂Y phase is formed.When Y content increases to 1.5wt%, the grain refinement effect is not obvious, and a large amount of Al₂Y phase aggregate in a network distribution at grain boundaries.The corrosion resistance of Mg-4Al-3Ca-0.7Mn-xY alloy can be improved by adding appropriate Y element.The corrosion resistance of the alloy is best when the addition amount of Y is 0.8wt%.