ABSTRACTCold rolling reduction, microstructural changes induced by cold rolling and subsequent heat treatment, hydrogen permeability (Φ) of Nb-Ti-Ni duplex phase alloys have been investigated using a rolling machine, a scanning electron microscope (SEM), an X-ray diffractometer (XRD) and a gas flow technique. The Nb-Ti-Ni alloys on the line connecting the TiNi compound and the Nb90Ti10 solid solution alloy show higher rolling reduction of 70 % or more at room temperature. The value of Φ for the Nb40Ti30Ni30 alloy, which is higher than that of pure Pd at 673K, decreases with increasing rolling reduction and attains to one third of that of the original one by the 50 % rolling reduction. The eutectic microstructure consisting of {TiNi+(Nb, Ti)} phases disappears and is replaced by the (Nb, Ti) phase embedded in the TiNi matrix by heat treatment 1073 K or more and for 605ks in a vacuum. However, its Φ value remains as it was by annealing at 1273 K or less, while it increases with increasing annealing periods at 1373 K or more and recovers to the original value after annealing for 605ks. These experimental results indicate that rolling and annealing techniques are the useful method for the preparation of a hydrogen permeable Nb-Ti-Ni alloy membrane.