Ordered mesoporous silica (MPS) with 1-10 nm pores has been evaluated for numerous applications in adsorption. As synthesized MPS is in powder form not suitable for membrane applications. Anodized alumina (AA) with 50-200 nm pores has been evaluated for membrane applications such as ultrafilration. The pores of AA is quite large to separate in molecular scale. In this project, we are interested in growing MPS in AA pores for enhanced separation at molecular scale. To elucidate the transport mechanisms in suchj a composite membrane, several small gas molecules have been used. The permeation of Argon through these membranes before and after calcination was performed using a batch method at temperature range between 253 K – 353 K and at low pressures. The MPS-AA before calcination was almost impermeable to Argon because the mesopores are blocked by the surfactant molecules. Upon calcinations, the Argon flux is substantial and can be used to examine the diffusion/permeation mechanism. The experimental flux through these membranes can be divided into different contributions and regimes such as surface diffusion, Knudsen diffusion, activated gaseous diffusion and viscous flow. A mathematical model is developed to interpret these contributions in terms of cross-sectional area of the pore channels or molecular mobility which can be suitably quantified by a physical property such as diffusivity. The temperature dependence of permeability is very useful to determine the mechanisms.