Electron irradiation induced nano-crystallization of melt-spun amorphous phase in Fe-Zr-B ternary alloys was investigated focusing on the difference in phase stability of amorphous phase during thermal annealing and electron irradiation. Nano-composite structure composed of nano-crystalline alpha-Fe precipitates with b.c.c.-structure, metallic Compounds and a residual amorphous matrix was formed under 2.0 MeV electron irradiation at 298 K, while such nano-structure was hardly realized by thermal annealing. The phase stability of an amorphous phase against electron irradiation was discussed based on the relationship between thermal properties and critical onset total dose of electron irradiation induced crystallization at 298 K.