Thermo-magnetic studies combined with transmission electron microscopy of and amorphous and nanocrystalline alloys revealed the precipitation of a single BCC -Fe nanocrystalline phase during the first stage of crystallization and the formation of intermetallic phases, the growth of -Fe nanograins and further precipitation of -Fe nanograins from the residual amorphous phase during the second stage of crystallization. The presence of 1 at% Cu in the second alloy accelerates the precipitation of the single nanocrystalline phase during the first stage of crystallization and facilitates further precipitation of -Fe nanograins from the residual amorphous phase during the second stage of crystallization.