The crystallization behavior and microstructure development of the Zr 61Al7.5Cu17.5Ni10Si4 alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr61Al7.5Cu 17.5Ni10Si4 alloy at 703 K, Zr2Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr2Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr 2Cu type crystalline phase. This indicates that the crystal growth of the Zr61Al7.5Cu17.5Ni10Si 4 alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr2Cu is 155 ± 20 kJ/mol in the Zr61Al7.5Cu17.5Ni 10Si4 amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr65Cu 35 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).