Fe73.5Cu1Nb3Si15.5B7 amorphous alloy undergoes a series of thermally induced structural transformations in temperature region between 25 and 800 degrees C, including structural relaxation, two Curie temperatures and crystallization. The changes in microstructure caused by these transformations are characterized in detail using XRD, TEM, Mossbauer spectroscopy and EDX elemental analysis. Mossbauer spectroscopy, in particular, reveals that there is a very small degree of crystallinity in the as-prepared alloy, which is lost during structural relaxation after annealing at temperatures below 400 degrees C. In addition, it suggests that crystallization of the alloy is much more complex process than suggested by XRD data, with several metastable intermediate phases serving as precursors to crystallization of stable crystalline phases. Magnetic, electrical and mechanical properties of the alloys are heavily influenced by the observed structural changes, most notably during crystallization of the alloy, where formation of crystalline phases and creation of new types of interfaces are the main factor to determine the performance of the alloy. (C) 2013 Elsevier B.V. All rights reserved.