Mixed matrix membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyvinyl alcohol based polar silica particles were prepared by solution casting technique. The homogeneity and thermal properties of the prepared PDMS-PU/silica membranes were characterized using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The SEM micrographs confirmed the distribution of silica particles in the polymer matrix without agglomerations. Gas permeation properties of membranes with different silica contents were studied for pure CO2, CH4, O2, He and N2 gases. The obtained results indicated the permeability of the condensable and polar CO2 gas was enhanced whereas permeability of other gases decreased upon increasing the silica content of the mixed matrix membranes. The permeability of CO2 and its selectivity over N2 was increased from 68.4 Barrer and 22 in pure PDMS-PU to 96.7 Barrer and 64.4 in the mixed matrix membranes containing 10 wt% of the silica particles.