We report magnetic and magnetoimpedance (MI) properties of as-quenched and Joule annealed (with and without external magnetic field) amorphous Co 73Fe4.5Ni0.5Mn0.5Nb 0.5Si4.2B16.8 alloy composition. The Joule annealing in the presence of magnetic field induces not only surface microstructural changes but also favourable anisotropy. Dc magnetic measurements show controlled annealing enhances soft magnetic nature of the sample. Virgin ribbons show MS ∼ 125 emu/g with μr ∼ 10 4 and exhibit large MI ratio of ∼100% at 3 MHz frequency. This MI ratio was further enhanced to 152% on Joule annealing (current density 0.85 × 107 A/m2) in the presence of applied magnetic field of 500 Oe. The field dependence MI shows a double-peak feature in as-spun ribbons, which is significantly enhanced for field annealed (FA) samples. The enhancement in MI and magnetic field sensitivity (η) in FA amorphous ribbons is attributed to the development of nanograins on the surface layer that strengthens the transverse magnetic structure. © 2014 AIP Publishing LLC.