Disordered nature of structural arrangement in amorphous and nanocrystalline alloys gives rise to advantageous soft magnetic properties in particular from a practical application viewpoint . Especially nanocrystalline alloys attract a lot of scienti?c interest because, contrary to their amorphous counterparts, their magnetic parameters do not substantially deteriorate at elevated temperatures during the process of their practical exploitation. To bene?t from their unique magnetic pr- erties, the mechanism of crystallization should be known. Here, we present the study of structural transformation of NANOPERM-type alloys by the help of Moessbauer spectrometry, conventional X-ray diffraction (XRD), and by an advanced diffraction of synchrotron radiation. 2 Experimental Alloys of the composition Fe Mo Cu B for x = 12, 15, 17, 20 prepared by 91?x 8 1 x 57 rapid quenching on a rotating wheel were analyzed in the as-cast state by Fe transmission Moessbauer spectrometry (TMS) and by conversion electron Moessbauer spectrometry (CEMS). The obtained as-quenched ribbons were about 10 mm wide and 20 ?m thick. The nanocrystalline state was achieved by annealing about 2 cm ? long samples for 1 h at temperatures up to 650 C in a vacuum. Conventional XRD was performed with Cu-K radiation in Bragg-Brentano con?guration with graphite ? monochromator in the diffracted beam. Monochromatic synchrotron radiation of 7keV(? = 0. 178 nm) provided at the KMC-2 beamline at BESSY Berlin was used for in situ examinations of structural transformations during continuous heat treatment.