Ferromagnetic (Fe0.76Si0.09B0.1P0.05)99−xNb1Cux (x=0, 0.25, 0.5, 0.75, and 1) bulk metallic glasses (BMGs) were synthesized by copper mold casting. The effects of Cu alloying on the glass-forming ability (GFA), microstructure, soft magnetic properties, and local subsurface deformation properties of this alloy series were investigated. The results showed that the addition of an appropriate amount of Cu led to the formation of α-Fe nanocrystals in the as-cast amorphous rods without obvious deterioration of the GFA. The enhancement of the soft magnetic properties of the representative (Fe0.76Si0.09B0.1P0.05)98.25Nb1Cu0.75 alloy was ascribed to α-Fe nanocrystals with a diameter of approximately 3nm, precipitating and dispersing randomly in the amorphous matrix. In addition, compared with the Cu-free base alloy, the subsurface deformation ability of the as-cast Cu-doped alloys was greatly improved by plastic shear deformation.