The results are presented of the study of the influence of the relaxation annealing at a temperature of 620 K for 2 h on the magnetoimpedance effect (MI) in amorphous Co66Fe4Nb2.5Si12.5B15 wires. It has been found that MI at low ac frequences noticeably increases after heat treatment, while it slightly changes at high frequences. Magnetoimpedance tomography has been used to show that this is related to that the changes in magnetic properties caused by heat treatment are different in various regions of a wire. In this case, the magnetic permeability of the surface region about 2.5 μm thick remains practically unchanged, but that of the inner regions significantly increases after annealing.