Pressure-Composition-Isotherm (PCT) measurements, in-situ small punch (SP) tests in hydrogen gas atmosphere and hydrogen permeation tests are conducted for Nb-W-Ta ternary alloys in order to investigate the alloying effects of tantalum on the hydrogen solubility, the mechanical properties and hydrogen permeability of Nb-5 mol%W alloy. It is found that the hydrogen solubilities of Nb-5 mol%W-Xmol%Ta (X=5, 10) alloys are very similar with that of Nb-5 mol%W alloy. Also, the mechanical properties in hydrogen gas atmosphere and hydrogen permeability of the alloys are comparable with Nb-5 mol%W alloy. Therefore, the addition of tantalum scarcely modifies the properties of Nb-5 mol%W alloys. Thus, it is not necessary to take into account the amount of tantalum in Nb-W alloys for hydrogen permeable membrane. In other words, it is not needed to remove tantalum impurity from niobium mineral ores in the course of the refinery process of niobium metal. This means that niobium mineral ore containing high tantalum impurity can be used to reduce the material cost of Nb-W-based hydrogen permeable membranes.