Formation of nano-structure in melt-spun ternary Fe-Nd-B alloys was examined focusing on electron irradiation induced crystallization. In Fe 82:2 Nd 7:1 B 10:7 (Fe/Nd/B = 23/2/3), Fe 77 Nd 4:5 B 18:5 and Fe 71 Nd 9 B 20 alloys, melt-spun amorphous phase changed to a crystalline phase during electron irradiation and nano-structure was formed. The crystalline phase in melt-spun Fe 86 Nd 9 B 5 and Fe 82:4 Nd 11:8 B 5:8 (Fe/Nd/B = 14/ 2/1) alloys was unstable under electron irradiation and electron irradiation induced amorphization occurred. With the further irradiation, crystallization from the amorphous phase was induced resulting in forming nano-crystalline structure. The onset total dose for the irradiation induced crystallization, namely, stability of the amorphous phase against electron irradiation depends strongly on the Fe-ratio, crystallization temperature, mismatch entropy and mixing enthalpy of the alloys.