Magnesium alloys are promising anode candidates for energy storage and conversion devices, which give rise to Mg-air batteries as the main development direction of next generation batteries. However, its commercial application still faces giant challenge. In this study, four types of Mg-xLa (La addition of 1, 3, 5, and 10 wt%) alloys with relatively high La content are prepared as anode materials for Mg-air batteries. The influence of La content on the microstructure and electrochemical performance are systematically investigated. All results indicate that adding 5 wt% La to Mg significantly improves the corrosion resistance and discharge activity, whilst excessive addition would accelerate self-corrosion rate due to the formation of large-area LaMg phase. The Mg-5La anode exhibits relatively high discharge platform and stable discharge process, and the specific discharge capacity is 1259.45 mAh g with the anodic efficiency of 57.67% at 20 mA cm. This boost can be explained by the ameliorative microstructure in Mg-5La anode, which reduces the extended self-corrosion of α-Mg phase and accelerates the spalling of corrosion products. This work might provide some basic meaningful data for designing the advanced anode materials for Mg-air batteries.