Mixed matrix membranes were prepared with polydimethylsiloxane (PDMS) and different weight percent surface-treated fumed silica (SiO2) to investigate the influence of SiO2 on transport behavior of O-2 and N-2 gases in the nanocomposite membranes. Fourier transform infrared spectroscopy (FTIR) showed that OH functional group on the surface of SiO2 was consumed upon incorporation of the silica into the polymer matrix. Thermogravimetric analysis (TGA) results revealed that SiO2-PDMS has improved thermal property over neat PDMS, supporting the argument that there is good interaction between the polymer and the fumed silica. Scanning electron microscopy (SEM) images of SiO2-PDMS membranes showed uniform dispersion of SiO2 nanoparticles in PDMS matrix. SiO2 nanoparticles disrupted and altered the PDMS polymer chains packing arrangement resulting in different membrane transport behavior of both O-2 and N-2 gases in SiO2-PDMS compared to the neat PDMS membrane. While the O-2 flux through SiO2-PDMS membranes was observed to increase with time, N-2 flux decreased with time before attaining steady state. The 10 wt%SiO2-PDMS membrane exhibited improved performance compared to neat PDMS membranes with O-2/N-2 selectivity and O-2 permeability increased from 2.43 to 3.46 and 590 Barrer to 640 Barrer, respectively, at 30 psig. This improvement is attributed to the influence of the well dispersed SiO2 nanoparticles in the PDMS matrix. (C) 2016 Elsevier B.V. All rights reserved.