The giant magneto-impedance of melt spun CoxFe72-xNb4Si4B20(x=10, 20, 36, 50) amorphous and nanostructured ribbons have been investigated. Alloys have been optimized at the driving current amplitude, frequency and found that amorphous ribbon of nominal composition of Co36Fe36Nb4Si4B20 shown maximum GMI ratio of 13%. The behaviour of the driving current amplitude on the GMI behaviour was studied and the sample was optimized for driving current amplitude, Iac=10 mA. The frequency dependence of the GMI behaviour was studied for the ribbon sample Co36Fe36Nb4Si4B20 at frequency in the range of 100 kHz-1.2 MHz of the optimized driving current amplitude and it was found that the sample showed the maximum GMI behaviour at f=700 kHz. The optimized samples were Joule heated at the current density J=0-35 A/m2 for a period of 1 min. The GMI ratio initially increased then progressively deteriorated with J, but after a certain range it shows up to 16% of improvement in the magneto-impedance value due the increase of nanocrystalline volume fraction. The asymmetry in the GMI profile was observed for the sample Joule heated at J=1-5 A/m2 for 1 min. © 2009.