The large changes of the impedance in soft magnetic alloys submitted to an external magnetic field caused a renewed interest due to perspective application in magnetic sensors. Magnetic relaxation effects are intrinsic properties of amorphous materials and may be detrimental to applications. In this work, the magnetoimpedance relaxation has been studied in melt-spun Co 6 8 . 2 5 Fe 4 . 5 Si 1 2 . 2 5 B 1 5 ribbons in a wide range of frequency (500kHz-6GHz). The low-frequency measurements have been performed using the classical volt-amperometric technique. In the high-frequency region, the magnetoimpedance relaxations have been studied measuring the reflection parameter S 1 1 of a coaxial line containing the magnetic sample by means of a vectorial network analyzer.