The frequency and the amplitude of the driving ac current dependence of the Giant Magneto-Impedance (GMI) behaviour in (Fe6 Co94)72.5Si12.5B15 amorphous wire have been studied. The single and two-peak behaviour in the GMI characteristics are observed which depends on the amplitude and frequency of the ac driving current flowing through the sample. The GMI ratio initially increased and then decreased monotonically with the increase of frequency, f, and the amplitude of the ac current, Iac. With the increase of amplitude of ac current, the response of the GMI voltage is found non-linear with the generation of higher harmonics. With the increase of higher harmonics, the first harmonic component of the GMI voltage started decreasing. With the increase of the ac current, the field sensitivity of the first harmonic components of the GMI voltage decreases and in higher harmonics it shows an increasing trend. The maximum field sensitivity was observed 7.5% per A/m for Iac = 2 mA and at frequency 100 kHz. The paper investigates the response of the second and third harmonics with the frequencies and amplitude of the driving current. A voltage equation derived from the rotational model to study the response of the GMI voltage. © 2005 Elsevier B.V. All rights reserved.