Amorphous silica membranes were deposited by thermal decomposition of tetraethoxtsilane(TEOS) at 600 ℃ on a γ-alumina coated stainless steel tube with pore size of 6-8 nm. During the CVD modification, forced cross flow through the porous wall of the support was very effective in plugging macropores. The silica membrane showed a hydrogen permeance of 3.5 × 10(-7) molㆍm(-2)ㆍs(-1)ㆍPa(-1) and a H2/N2 selectivity of about 10 at a permeation temperature of 450 ℃. The CVD-modified silica membrane was stable in a H2-N2 mixture of 450 ℃ for 100 hour.