NOVELTY - Hydrogen permeation separation thin film comprises nickel-titanium-niobium alloy having component composition, and alloy structure dispersed in substrate. The component composition comprises (at.%) niobium (10-47), titanium (20-52), nickel (20-48 at.%), and unavoidable impurity. The alloy structure has fine grain of niobium group solid solution alloy. Nickel and titanium form a solid solution in niobium of niobium group solid solution alloy. The substrate comprises nickel titanium (niobium) intermetallic compound.    USE - The hydrogen permeation separation thin film is useful for chemical reaction processes, e.g. steam reforming process of hydrocarbon and hydrogenation/dehydrogenation processes, e.g. benzene-cyclohexane reaction. The hydrogen permeation separation thin film can also be used purifying hydrogen gas used as fuel gas of energy systems, e.g. hydrogen fuel, battery, and hydrogen gas turbine.    ADVANTAGE - The thin film exhibits excellent hydrogen permeation performance, and provides high mechanical strength. The thin film has stable alloy structure. The thin film has reduced thickness while provide excellent performance for long period of time.    DETAILED DESCRIPTION - Hydrogen permeation separation thin film comprises nickel-titanium-niobium alloy having component composition, and alloy structure dispersed in the substrate. The component composition comprises (at.%) niobium (10-47), titanium (20-52), nickel (20-48 at.%), and unavoidable impurity. The alloy structure has fine grain of niobium group solid solution alloy. Nickel and titanium form a solid solution in niobium of niobium group solid solution alloy. The substrate comprises nickel titanium (niobium) intermetallic compound. The nickel titanium (niobium) intermetallic compound is subjected to solid solution containing of titanium in nickel titanium intermetallic compound in the state where niobium is substituted by refining heat processing material of casting foil material less than 0.07 mm thick using chill roll method.    DESCRIPTION OF DRAWING(S) - The figure shows scanning electron microscope view of nickel-titanium-niobium alloy of hydrogen permeation thin film.