Using of nanocomposite membranes composed of polymer and inorganic nanoparticles is a novel method to enhance gas separation performance. In this study, membranes were fabricated from polyester (PE) containing silica (SiO2) nanoparticles and gas permeation properties of the resulting membranes were investigated. Morphology of the membranes, SiO2 distribution and aggregates were observed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis. Furthermore, thermal stability, the residual solvent in the membrane film, and structural ruination of membranes were analyzed by Thermo Gravimetric Analysis (TGA). The effects of SiO2 nanoparticles on the glass transition temperature (Tg) of the prepared nanocomposites were studied by Differential Scanning Calorimetry (DSC). The results obtained from gas permeation experiments with a constant pressure setup showed that adding SiO2 nanoparticles to the polymeric membrane structure increased the permeability of the membranes.