The hydrogen-induced phase separation of Cu–Zr binary amorphous alloys during hydrogen gas charging at elevated temperature was demonstrated; the homogeneous binary alloy was decomposed into pure Cu and Zr-hydride by absorbing hydrogen into the structure. The decomposition, which is attributed to the opposed affinity to hydrogen of Cu and Zr, took place in nanometer scale. The hydrogen absorption kinetics was compared for the alloys with different compositions. The structure after hydrogen absorption was analyzed using x-ray diffraction, ultra-small and small angle neutron scattering, and electron microscopy.