The microstructure and hydrogen permeability of the Nb40Hf30Ni30 ternary alloys were investigated in particular. The as-cast Nb40Hf30Ni30 alloy consists of the bcc- (Nb,HF) solid solution, the B-f-HfNi compound and the fine eutectic phase of {(Nb,Hf) + HfNi}. The annealed Nb40Hf30Ni30 alloy consists of the bcc-(Nb, Hf) solid solution and the fine eutectic phase of {(Nb,Hf) + HfNi}. The as-cast Nb40Hf30Ni30 alloy shows a high Phi value of 4.3 x 10(-8) [mol H-2 m(-1) s(-1) Pa-0.5] at 673 K, and for the annealed Nb40Hf30Ni30 alloy, the Phi value is 3.8 x 10(-8) [mol H-2 m(-1) s(-1) Pa-0.5] at 673 K. Annealing can't enhance the hydrogen permeability of the Nb40Hf30Ni30 ternary alloy. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.