Phase transformation behavior and phase stability of Zr 66:7 Cu 33:3 metallic glass were examined during thermal annealing and electron irradiation. Metastable f.c.c.-Zr 2 Cu phase precipitated in amorphous matrix and formed nanostructure by electron irradiation induced crystallization. With further thermal annealing, the nano grains of the f.c.c.-Zr 2 Cu coarsened accompanied by precipitation of thermally stable b.c.t.-Zr 2 Cu phase from amorphous matrix. The thermal equilibrium b.c.t.-Zr 2 Cu crystalline phase was transformed to the nanocrystalline f.c.c.-Zr 2 Cu phase through the amorphous state during electron irradiation. The unique solid state amorphization and crystallization behavior by electron irradiation can be explained by the thermodynamical model based on the change in relative phase stability among amorphous and crystalline phases by electron irradiation. The thermal stability of the f.c.c.-Zr 2 Cu phase and the effect of dose rate on electron irradiation induced phase transformation were investigated in order to confirm the validity of the thermodynamical model.