In this paper we present dc magnetization, ac susceptibility and impedance measurements on amorphous alloy ribbons Co 80-x Fe x B 10 Si 10 with x = 0, 6, 8 and 10 at.%. They indicate that at room temperature these samples have good soft magnetic behavior including the giant magneto-impedance effect. The real part of the ac susceptibility χ’ ac reveals an irreversibility field, H irr , which corresponds to the transverse anisotropy field, H k , at which the magneto-impedance ratio reaches its maximum value.