Tungstates Ln(6)WO(12) are proton conducting crystalline materials which show significant mixed protonic and electronic conductivity and stability in moist CO2 environments. These materials are promising candidates for hydrogen separation membranes at temperatures above 700 degrees C, especially when integrated in intensified processes as catalytic membrane reactors. From this family of compounds, La6-x WOy (0.4 < x < 0.7) presents the highest protonic conductivity and hydrogen permeability. This contribution presents the preparation, hydrogen permeation and stability study of La5.5WO11.25-delta membranes. Hydrogen separation properties of La5.5WO11.25-delta were systematically analyzed, i.e. the influence of the H-2 concentration in feed stream, humidification degree and operating temperature were investigated. The integrity of the La5.5WO11.25-delta after the hydrogen permeation experiments was confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The stability of La5.5WO11.25-delta, permeation when CO2 containing atmosphere was used as sweep gas was evaluated. Furthermore, the stability of this compound in CO2-rich and sulfur-containing environments was confirmed by XRD. (C) 2013 Elsevier B.V. All rights reserved.