This study examined the amorphization behavior and thermal stability of mechanically alloyed Ni57Zr20Ti18Al5 alloy powders synthesized by high-energy ball milling. Complete amorphization is feasible after 5h of milling. The thermal stability of the Ni57Zr20Ti18Al5 amorphous powders was investigated by differential thermal analysis. As the results demonstrated, the temperature interval of the supercooled liquid region defined by the difference between glass transition temperature (T-g) and crystallization temperature (T-x), i.e., DeltaT (=T-x - T-g) is 54 K for Ni57Zr20Ti18Al5. The glass transition and crystallization temperatures of mechanically alloyed samples are different from those reported in the literature for samples prepared by melt spinning techniques. The different thermal stability is believed to be due to the introduction of impurities into the ball-milled samples during mechanical alloying process. The glass transition behavior in the Ni57Zr20Ti18Al5 is found to be a kinetically modified thermodynamic phase transformation process. (C) 2003 Elsevier B.V. All rights reserved.