The influence of isothermal annealing on the magnetisation process in strong magnetic fields of the amorphous Fe61Co10Y8Ni1B20 alloy ribbons was investigated. Samples in the form of ribbons were produced by rapid quenching of liquid alloy on a rotating copper wheel. In order to study the relaxation process, the investigated Fe61Co10Y8Ni1B20 samples were subjected to annealing below the crystallisation temperature at 700 K for 1 h and then at 770 K for 3.5 h. The structure of the samples was examined by X-ray diffraction measurements (XRD). It was found, that all of measured samples in the as-cast state and after thermal treatment, were amorphous. On the basis of virgin magnetisation curve analysis, the type, size and density of structural defects occurring in the investigated samples were determined. It was found that after the first stage of annealing, decay of linear defects (pseudo-dislocation dipoles) into smaller, more thermodynamically stable, point defects occurs. The presence of point like defects was also confirmed after the second stage of annealing.