Amorphous phases in the completely immiscible Bi‐Fe system were formed for the first time by ion mixing and magnetron cosputtering. In the ion mixing experiments, multilayer samples of Bi and Fe were bombarded with energetic Fe ions. In the planar magnetron cosputtering, mixture films were prepared by simultaneously sputtering Bi and Fe atoms onto the substrates kept at liquid‐nitrogen temperature. Using Rutherford backscattering spectrometry and transmission electron microscopy, the compositions and phases of the thin alloy films were identified. The amorphous alloy formed by ion mixing is Bi50Fe50. The composition of the amorphous alloy films formed by magnetron cosputtering is in the range of 40–60 at. % Bi.