The crystallization behaviour of Fe 70.8 Nb 3.7 Cu 1 Al 2.7 Mn 0.7 Si 13.5 B 7.6 alloy prepared in the form of amorphous ribbons by melt-spinning technique was studied using differential scanning calorimetry and the temperature variation in resistivity. An X-ray diffaction and transmission electron microscopy study showed the formation of f -Fe and/or Fe 3 nanoparticles after the first stage of crystallization. The activation energy for this nanophase formation was 68 kcal mol m 1 . The brittleness (...) of the alloy increased with the formation of nanoparticles after heat treatment. Superior soft magnetic properties were achieved when the material was heat treated at 790 K for 15 min. The particle size at the optimum heat treatment condition for superior soft magnetic properties was found to be 6.0 - 0.5 nm which was less compared than for the Fe-Nb-Cu-Si-B system. The observed coercivity value at the optimum heat treatment condition was found to be 0.32 A m m 1 . The presence of Al in the alloy reduced the particle size and the magnetic anisotropy energy of the system, which resulted in superior soft magnetic properties of the heat-treated materials. (shrink)