In order to develop alloys combing high hydrogen permeability with large resistance to the hydrogen embrittlement, microstructures and hydrogen permeability (Phi) have been investigated for the as-cast alloys on the straight line connecting the eutectic {TiCo + (Nb, Ti)} phase and the Nb-rich primary (Nb, Ti) phase in the Nb TiCo system. The alloys on the above-mentioned line consist of the TiCo compound and the (Nb, Ti) solid solution. The value of Phi increases with increasing temperature and volume fraction of the primary (Nb, Ti) phase. The most Nb-rich Nb60Ti21Co19 alloy shows the highest Phi value of 3.99 x 10(-8) (mol H(2)m(-1) s(-1) Pa-0.5) at 673 K, which is 2.6 times higher than that of pure Pd. The present work demonstrates that highly hydrogen permeable alloys are obtainable in the Nb rich Nb-Ti-Co ones on the straight line connecting the eutectic {TiCo + (Nb, Ti)} phase and the Nb-rich primary (Nb, Ti) phase. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.