Formation of nano-structure in melt-spun ternary Fe-Nd-B alloys was examined focusing on electron irradiation induced crystallization. In Fe82.2Nd7.1B10.7 (Fe/Nd/B = 23/2/3), Fe77Nd4.5B18.5 and Fe71Nd9B20 alloys, melt-spun amorphous phase changed to a crystalline phase during electron irradiation and nano-structure was formed. The crystalline phase in melt-spun Fe86Nd9B5 and Fe82.4Nd11.8B5.8 (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.