Ultrathin ( < 1 mu m) Pd-Ag alloy membranes have been successfully coated on the internal surface of YSZ-mixed Al2O3 hollow fibers by sequential electroless plating. The H-2 permeance and selectivity of internally-coated (0.8 mu m thick) Pd-Ag alloy membrane is more than 5 mu mol m(-2) s(-1) Pa-1 and well over 1200, respectively, at 450 degrees C and the pressure difference of 100 kPa. The internally-coated Pd-Ag alloy membranes exhibit the significantly improved thermal stability and durability of membranes. This is due to the support layer constrains the thermal expansion of Pd-Ag alloy during the annealing as well as the permeation tests, preventing the clelaminating of Pcl-Ag alloy membrane, and hence allowing the membranes to tolerate the repeated cyclic permeation tests over at least 5 cycles (10 h/cycle) without the significant loss of H-2 selectivity. Moreover, mechanical damages (e.g., scratching) of Pd-Ag membrane can also be prevented as the Pd-Ag membrane is not exposed directly to the external surface. (C) 2013 Elsevier B.V. All rights reserved.