Porous glass monoliths are suitable model systems to study pore size-related effects in gas diffusion. Here, mesoporous glass membranes with different surface properties and pore diameters covering the lower mesopore range were synthesized and used to study gas permeation of adsorbable and non-adsorbable gases. Dynamic single gas permeation measurements were performed using a modified Wicke-Kallenbach cell. Chemical surface modification of the inner surface of the membranes resulted in altered adsorption and diffusion properties.