Amorphous Co68.15Fe4.35Si12.5B15 alloy ribbons were treated by low-frequency pulsing magnetic field. M?ssbauer spectroscopy and TEM observation show that initial nano-crystallization of the amorphous samples occurs, and the volume fraction of crystallized phase has a relation with pulsing magnetic field intensity. The giant magnetic impedance (GMI ) of the samples were tested by a GMI instrument; the results show a non-monotonic change between GMI and pulsing magnetic field intensity HP, and the GMI reaches the greatest value of 263.5% under the magnetic field intensity HP=350 kA·m-1. The transverse anisotropy induced by pulsing magnetic field in specimens affects the GMI effect. When the external dc current magnetic filed Hex is equal to Hk, GMI reaches the peak value