Supercooled liquid region (Delta T-x), tensile fracture strength (sigma(f)), and Vickers hardness (Hv) of Fe-B-Zr-Nb amorphous alloys were measured. The addition of Nb to the ternary Fe-B-Zr system was found to lead to significant changes in glass-forming ability (GFA), strength, and hardness. The results are discussed in the context of the three empirical rules for achievement of high GFA metallic glass and the change in packing density of the amorphous phases.