Cobalt-based metallic glasses have stimulated widespread interest due to their excellent mechanicalproperties and soft magnetic behavior. In the present work, a new Co51Fe15Hf6.5B27.5glassy alloy wasdesigned based on the ternary eutectic Co66Hf6.5B27.5composition and its microstructure, thermalbehavior and magnetic properties were examined. Partial substitution of Co with Fe in the new alloysystematically changes the crystallization behavior, enhances the fraction of complex (Co,Fe)21Hf2B6phase upon crystallization and increases the extension of the supercooled liquid region from 26 K to48 K. The improved thermal stability is in line with an increased activation energy of crystallization from523±20 kJ/mol for the Co66Hf6.5B27.5glass to 573±20 kJ/mol, corresponding to the Co51Fe15Hf6.5B27.5glass. Magnetic studies revealed that the addition of Fe noticeably increases the saturation magnetiza-tion, Curie temperature, and slightly increases the coercive force from 19 A m2/kg to 57 A m2/kg, 315 Ke515 K and 0.5 A/m to 1.5 A/m, respectively. It was found that the Co51Fe15Hf6.5B27.5glassy ribbonsexhibit a high resistance against milling-induced crystallization under cryogenic condition. The preparedcryomilled glassy particles show adequate thermal stability and thermoplastic forming ability for hotconsolidation into a high density (96%) bulk metallic glass (BMG) with 10 mm diameter. TheCo51Fe15Hf6.5B27.5BMG exhibits a saturation magnetization of 57 A m2/kg, a Curie temperature of 527 Kand a very low coercivity of 7 A/m, indicating its superior soft magnetic performance compared to mostCo/Fe-based BMGs fabricated via powder metallurgy techniques. The evolution of microstructure,thermal behavior and magnetic properties upon cryomilling, hot consolidation and subsequentannealing was discussed.