To investigate transport properties of Mo-substituted Nd5.4Mo0.3W0.7O12-delta for hydrogen separation application, hydrogen fluxes of Nd5.4Mo0.3W0.7O12-delta have been measured in both dry and wet sweep gases. The fluxes in dry sweep gas show lower temperature dependence at high temperatures than at low temperatures. Comparing the hydrogen permeability among rare earth tungstates, it has been revealed that the larger the RE-site cation radius, the higher the hydrogen permeation. Water splitting effect for the wet sweep gas has been confirmed by mass spectrometry. Oxygen surface kinetics under oxidizing conditions has been studied by ToF-SIMS measurements, and is significantly faster under wet conditions than dry. Hydration kinetics has been studied by conductivity relaxation measurements under reducing conditions for the first lime, showing a two-fold non-monotonic behavior. (C) 2014 Elsevier B.V. All rights reserved.