Abstract We have synthesized Fe-Ni-B amorphous nanoparticles by chemical reduction of the transition metal solution. A compositional study shows that the nominal Ni/Fe ratio is preserved. The new preparation method used yields a much higher boron composition than the one obtained traditionally by rapid quenching and other chemical synthesis previously reported. For all compositions, the size of the particles is about 2.1 nm diameter with a narrow log-normal distribution.