The effect of simultaneously adding P and Cu on the crystallization behavior of hetero-amorphous FeSiB alloy was investigated. Thermal properties and microstructure evolution were Studied by means of X-ray diffraction, transmission electron microscopy, differential scanning, and isothermal calorimetric methods. It is found that the addition of P and Cu to the FeSiB alloy changes its crystallization temperature as well as the apparent activation energy for crystallization. The crystallization process is mainly dominated by three-dimensional growth with various nucleation rates for the selected FeSiB(PCu) alloys. The phases formed during crystallization for the different alloys of Fe84Si4B12, Fe83.3Si4B12Cu0.7, and Fe83.3Si4B8P4Cu0.7 are similar. The refinement effect of adding P and Cu to the FeSiB alloys is observed. The mean size of alpha-Fe phases decreases from 200 nm to about 20 run. [doi: 10.2320/matertrans.M2009206]