The hydrogen permeability have been measured for pure niobium and Nb-5 mol%X (X = Ru and W) alloys in order to investigate the alloying effects of ruthenium and tungsten on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, J . d, and the difference of hydrogen concentration, Delta C, between the inlet and the outlet sides of the membrane. it is found that the addition of ruthenium or tungsten into niobium increases the hydrogen diffusion coefficient during the hydrogen permeation. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. it is interesting that the activation energy for hydrogen diffusion is decreased by alloying of ruthenium or tungsten into niobium. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.