In order to improve the stability of silica membranes against water (vapor) some metal oxides were added to silica to obtain composite silica-metal oxide membranes by the sol-gel techniques. A Ni-doped silica membrane (Ni/Si=1/2) fired at 500°C showed a relatively large permeance of 1.5×10−5 [m3(STP)/(m2skPa)] with selectivity of 350 (H2/CH4), 4200 (H2/SF6) at 200°C and 100 (CO2/CH4) at 35 °C. After leaving the membrane in humid air (RH: 60%, 40°C) for 70 days, the permeance of H2 decreased by about 50% but the selectivity was improved to 930 for H2/CH4. And little change was observed in the activation energy for H2 permeation, while under the same conditions a silica membrane showed a quite large change in the activation energy from 3.1kJ/mol to 14kJ/mol. There is a possibility that metal oxides added to silica help prevent the densification of silica networks through which hydrogen and helium molecules can permeate.