Abstract: Mg-5Al-4Ca-0.8Mn alloy was modified with rare earth Ce.The effects of the Ce addition on the microstructure and mechanical properties of Mg-5Al-4Ca-0.8Mn alloy were investigated by OM, SEM, hardness test and tensile test. The results show that Ce has a good effect on the modification of Mg-5Al-4Ca-0.8Mn alloy. When the Ce content is 0.8%, the grain boundary of the alloy is clear, the uniformity is best, and the microstructure refinement effect is best. When the Ce content is increased to 1.2%, the microstructure refinement effect of the alloy is weakened. With the increase of Ce content, the hardness, tensile strength and elongation of the Mg-5Al-4Ca-0.8Mn alloy increase first and then decrease. The hardness, tensile strength and elongation of the alloy with 0.8%Ce content all reach the maximum values, and the comprehensive mechanical properties are best.