The corrosion resistance of Fe–M–B–Cu alloys in which M is a transition metal of two first series, particularly concerning the effect of composition and also concerning the affect of corrosion on magnetic properties have not been evaluated. In this paper, the effect of composition and partial crystallization on corrosion resistance of Fe₈₀Nb_3.5Zr_3.5B₁₂Cu₁, Fe₈₀Nb_3.5Mo_3.5B₁₂Cu₁, Fe₈₀Zr_3.5Mo_3.5B₁₂Cu₁ and Fe₈₀Mo₇B₁₂Cu₁ amorphous alloys and its effect on saturation magnetic flux density, B_s, were investigated using 0.1 M H₂SO₄ solutions. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and potentiostatic polarization. Greater corrosion resistance is observed in alloys with Nb addition and the smaller resistance in alloys containing only Mo. The alloy with Zr and Mo has an intermediate corrosion resistance. This result was related to the protective passive film of the alloys. Crystallization decreases the corrosion resistance of the amorphous alloys for every composition analyzed. The decrease in saturation magnetic flux density, B_s, with immersion in a corrosive solution and a dependence of this decrease as corrosion resistance of alloys analyzed, show that control of the corrosion phenomena in these alloys is necessary for applications in which the magnitude of B_s is important.