Abstract: The magnesium alloy with medium and low rare earth content, fabricated by wire and arc additive manufacturing（WAAM）, is expected to achieve excellent mechanical properties through direct aging treatment.The Mg-5Gd-2Y-0.4Zr alloy was fabricated by the WAAM, and its microstructure and mechanical properties under direct aging heat treatment were studied. The results indicate that the as-deposited alloy exhibits a fine grain size（≤26μm）, a high content of alloying elements in the matrix, and few intergranular second phases. After direct aging treated at 200℃ for 128h, the hardness of direct aging treated alloy increased from（63.3±2.2）HV_0.3 to（85.1±2.1）HV_0.3,reaching 95.6% of the hardness sf solution + aging treated alloy; while the tensile strength and yield strength increased from（217.3±2.8）MPa and（91.0±7.7）MPa to（240.3±1.6）MPa and（130.9±2.5）MPa, respectively.In conclusion, this study demonstrates that direct aging treatment has a remarkably strengthening effect on the mechanical properties of Mg-5Gd-2Y-0.4Zr alloy.