Amorphization behaviour of NixTa100-x alloy powders synthesized by mechanical alloying mixtures of pure crystalline Ni and Ta powders with a Spex high energy ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. This range is larger than amorphous alloys prepared by the rapid-quenching process or by electron-gun deposition technique. A supersaturated nickel solid solution formed for Ni-rich composition. The thermal stability has been investigated by differential thermal analysis. The crystallization temperature of amorphous Ni-Ta powders was proportional to the Ta content, and the activation energy of amorphous Ni-Ta powders exhibited a maximum near the eutectic composition. It is found that the amorphization rate at the early stage of the mechanical alloying process was faster in the intermediate compositions than those at both Ni-and Ta-rich compositions.