Silicon based particles were synthesized by using tetraethoxysilane (TEOS) as silica precursor, and low concentration of cetyltrimethyl ammonium bromide (CTAB) with polyvinyl alcohol (PVA) as templating agents. The synthesized particles had a higher hydrophilicity and polarity than conventional silica particles. PU and PU/silica composite membranes were prepared by solution casting technique. Hybrid membranes were characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning calorimetery (DSC). FT-IR result indicated the existence of PVA in the final structure of silica network. The SEM micrographs confirmed the nano-scale distribution of silica particles in the polymer matrix. Gas permeation properties of membranes with different silica contents, was studied for pure CO2, CH4, O-2 and N-2 gases. The results showed an increase in the solubility and a corresponding reduction in the diffusivity of the gases through the membranes by increasing the silica content in the polymer matrix; consequently, the permeability of the condensable and polar CO2 gas was enhanced whereas that of other gases decreased. In the membrane with 10 wt% silica content an enhancement of CO2/CH4 (alpha approximate to 10.1) and CO2/N-2 (alpha approximate to 70.7) selectivities was observed. Finally, the experimental permeability values were compared with theoretical predictions based on gas solubility and diffusivity. (C) 2013 Elsevier B.V. All rights reserved.