Magnesium-based metallic glasses (MMGs) show intriguing potentials for application as implantable biomaterials owing to their disordered atomic structure, good biodegradability, low elastic modulus, high strength, and large elasticity. However, despite of all these advantages, their brittleness is their Achilles’ heel, which severely limits their application as biomedical materials. In the current study, a significantly improved ductility of MMGs under bending and tensile loading through minor alloying with rare-earth element ytterbium (Yb) at an atomic concentration of 2 and 4% is reported. The enhanced ductility is attributed to the increased density of shear bands close to fracture end and larger plastic zones on the fracture surface. In comparison with that of Yb-free control, in vitro cell culture study confirms an improved biocompatibility of MMGs alloyed with Yb as determined by MTT, live-dead, and cytoskeleton staining assays, respectively.