Ni-doped silica membranes of various Ni contents (Si/Ni = 0-1/1) were prepared on porous SiO2-ZrO2 composite intermediate layers (Si/Zr = 1/1) by the sol-gel techniques to test their hydrothermal stability and gas permeation characteristics in steam at high temperatures (steam: 90-400 kPa, 500 degrees C). Preceding firing of the intermediate layer and the Ni-doped silica layer in steam at higher temperatures (steam: 90 kPa, 650 degrees C) before exposed to hydrogen at high temperatures was found to drastically improve the hydrothermal stability of Ni-doped silica membranes in steam, showing, for example, a steady permeance of He around 1.7 x 10(-5) [m(3)(STp)(.)m(-2.)s(-1.)kPa(-1)] with high selectivity of 1150 (He/N-2) in steam (steam: 90 kPa, 500 degrees C), which did not change largely even in steam of higher pressure (steam: 400 kPa, 500 degrees C). It was also found that the membrane selectivity could be further improved with negligible decrease in H-2-permeance by firing the membranes after impregnating dilute aqueous NiNO3 solution.