The lightweight Mg 65 Cu 7.5 Ni 7.5 Zn 5 Ag 5 Y 10 bulk metallic glasses (BMG) always fail before yielding, with irreproducible strengths <650MPa. Adding particles of TiB 2 as the reinforcing phase, which can be uniformly distributed in the matrix without adversely affecting its glass-forming ability upon copper mold casting, the BMG composites can sustain a plastic strain to failure of 2–3% at a compressive fracture strength as high as 1.3GPa. The strengthening/toughening effects of the second phase particles are attributed to their ability to serve as obstacles to the propagation of run-away shear bands and micro-cracks, as well as to the generation of multiple shear bands due to the large elastic mismatch between the TiB 2 and the matrix. The angle between the compressive shear plane and loading axis is ∼41°, consistent with the Mohr–Coulomb criterion. The very high specific strength of ∼3.5×10 5 Nmkg −1 exceeds by far those of commercial Mg or Al alloys and even Zr-based BMGs.