Silver-doped methyl-modified silica membranes (Ag/M-SiO2) have been prepared using the sol-gel method by adding AgNO3 solution to a methyl-modified silica sol. The influence of silver-doping on the physical and chemical structures, thermal stability of -CH3 groups, and gas permeation performance for the silica membranes were investigated. The metallic silver results from the reduction of AgNO3 which can be completely transformed after calcined above 200 degrees C. The Si-CH3 vibrational bands disappear completely when the calcination temperature is increased to 600 degrees C, which mineralized when the calcination temperature is further increased to 750 degrees C. The doping of silver nanoparticles has nearly no influence on the chemical structure of the methyl-modified silica materials and the thermal stability of -CH3 groups, but can make the mean pore size, total pore volume, H-2 permeability, and H-2/CO2 selectivities of the silica membranes increase. When operated at 200 degrees C and a pressure difference of 0.35 MPa, the H-2 permeance and H-2/CO2 selectivity of Ag/M-SiO2 membrane with the AgNO3/tetraethylorthosilicate molar ratio of 0.08 is 8.99 x 10(-6) mol . m(-2) . Pa-1 . s(-1) and 10.22, respectively. After hydrothermal treatment and regeneration, the Ag/M-SiO2 membranes show a smaller change in gas permeances and H-2/CO2 permselectivities than the methyl-modified silica membranes without silver-doping.