Sol-gel derived silica membranes are reviewed in terms of control of silica network size and hydrothermal stability, which are most important issues for a practical application of amorphous silica membranes in industry. For control of silica network size, organic-template and spacer methods are introduced. Bridged alkoxides with organic groups between 2 Si atoms can be used for control of silica network size by both template and spacer method, for example, BTESE-derived silica membranes showed quite high hydrogen permeance with high H² to SF⁶ permeance ratio of 1,000 due to loose organic-inorganic silica networks by Si-C-C-Si unit. For hydrothermal stability of amorphous silica membranes at high temperatures, metal-doped silica membranes are introduced, especially Ni- and Co-doped silica membranes with superior hydrothermal stability and hydrogen permeation performance. Finally, recent progresses in metal-doped silica membranes such as Nb-SiO² and Pd-SiO² are also summarized.