The H-2 permeability of the Pd-Cu alloy foil with a body-centered cubic (bcc) structure has been studied at high temperatures available to membrane reactors. The permeability of the foil containing 54 wt.% Pd drastically decreases at 625 degrees C, but it is immediately restored at 600 degrees C within I h. The restoration is probably due to the phase transition from face-centered cubic (fcc) to the bcc structure. In contrast, the permeability gradually decreases at 600 C with the foil containing 56 wt.% Pd, then gradually recovers at 575 degrees C. The permeability of the foil containing 60 wt.% Pd also gradually decreases at 500 degrees C and the formation of the fcc phase partially occurs in the bcc phase accompanying the compositional heterogenization. The permeability of the bcc alloy decreases with a decrease in the Pd content probably due to the decrease in the hydrogen solubility. The activation energy of the H-2 permeability increases with the decrease in the Pd content. The permeability gradually decreases after storing the bcc foil under flowing Ar, suggesting that the hydrogen solubility is gradually decreased in the absence of gas-phase hydrogen. (C) 2014 Elsevier B.V. All rights reserved.