A Mo-substituted lanthanum tungstate mixed proton-electron conductor, La5.5W0.6Mo0.4O11.25- (LWM04), was synthesized using solid state reactions. Dense U-shaped LWM04 hollow-fiber membranes were successfully prepared using wet-spinning phase-inversion and sintering. The stability of LWM04 in a CO2-containing atmosphere and the permeation of hydrogen through the LWM04 hollow-fiber membrane were investigated in detail. A high hydrogen permeation flux of 1.36 mL/min cm(2) was obtained for the U-shaped LWM04 hollow-fiber membranes at 975 degrees C when a mixture of 80% H-2-20% He was used as the feed gas and the sweep side was humidified. Moreover, the hydrogen permeation flux did not significantly decrease over 70 h of operation when fed with a mixture containing 25% CO2, 50% H-2, and 25% He, indicating that the LWM04 hollow-fiber membrane has good stability under a CO2-containing atmosphere. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 1997-2007, 2015