The glass-forming ability and magnetic properties of (Fe, Co)-B-Si-Nb glassy alloys have been investigated. The maximum diameter for the formation of a glassy alloy rod was 2.0 mm for Fe72B20Si4Nb4 and 4.0 mm for (Fe0.5Co0.5)72B20Si4Nb4. A number of local-ordered regions are recognized in Fe72B20Si4Nb4 bulk glassy alloy by high-resolution transmission electron microscopy. However, no local-ordered regions are observed in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy. Saturation magnetization, coercive force, and maximum permeability were 1.14 T, 1.5 A/m, and 32 000, respectively, for the (Fe0.6Co0.4)72B20Si4Nb4 bulk glassy alloy. [ABSTRACT FROM AUTHOR]