In this work, an Fe-Ni-P-Si melt-spun amorphous alloy is obtained and mechanically alloyed under two milling conditions. The morphology, structure and thermal behavior was analyzed as a function of milling time and conditions. The milling process is able to separate the amorphous phase in different phases. This separation gives a paramagnetic Fe poorer phase and the formation of (Fe,Ni) phosphides with some remains of the amorphous original phase. Furthermore, small contamination from the milling tools was detected. The calorimetric analysis confirms the existence, on heating, of a recovery process and several crystallization processes. The low energy milling conditions favors a less important relaxation process and a high thermal stability of the amorphous phase. Thus, the time interval between the onset temperature of the structural relaxation and the first main crystallization is higher, favoring ulterior thermal annealing to obtain a mixture of an amorphous phase and a nanocrystalline alloy with controlled size grain.