To examine the effects of Yb addition on wrought Mg alloys, this study evaluates the influence of Yb content (0%-1.0%, mass fraction) on the microstructure, room-temperature, and high-temperature mechanical properties of the Mg-9Gd-4Y-1.2Zn-0.3Zr (mass fraction, %) alloy (GWZK). Mechanical performance tests and microstructural characterizations were conducted on alloy samples after solid solution treatment, extrusion, and aging. The results reveal that the GWZK-0.2Yb alloy exhibits superior mechanical properties, achieving tensile yield strength (TYS) of 456 MPa, which is an increase of approximately 45 MPa compared to the Yb-free GWZK-0Yb sample, and an ultimate tensile strength of 509 MPa. Furthermore, at 250 ^oC, the GWZK-0.2Yb alloy demonstrates a high yield strength of 326 MPa and ductility of 10.6%, indicating a synergistic improvement in strength and plasticity relative to the Yb-free sample. Microstructural analysis shows that the addition of 0.2%Yb suppresses the formation of long-period stacking ordered (LPSO) phases in the GWZK alloy while promoting the precipitation of β′ and γ′ phases during aging. The enhancement in strength is primarily attributed to the lamellar LPSO within the α-Mg matrix post-aging, as well as the dense precipitation of β′ and γ′ phases. However, increasing the Yb content to 0.5% reduces ductility at both room and high temperatures, primarily due to the high volume fraction of brittle β phases. Further increasing the Yb content to 1.0% leads to simultaneous decrease in strength and ductility at both temperature ranges. This degradation is attributed to the increased presence of the β phase, which reduces the number density of β′ and γ′ phases precipitated during the aging of the GWZK-1.0Yb alloy.