Mixed matrix membranes (MMMs) were developed by incorporating inorganic silica nanoparticles into blends of polysulfone/polyimide (PSF/PI) asymmetric membranes for gas separation using phase inversion technique. The membranes were characterized by using scanning electron microscopy (SEM), Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA). SEM results show different morphologies of surfaces and cross-sections of the membrane where agglomeration is observed at 20.1 wt.% silica loading. TGA analysis indicates good thermal stability of the hybrid membranes. Permeation results show that CO2 permeance increased with the introduction of 5.2 wt.% silica contents (73.7 +/- 0.2 CPU) in PSF/PI-20% blend and it increased with the increase in silica contents. With 15.2 wt.% silica contents, the highest permselectivity of alpha(CO2/CH4) = 61.0 +/- 0.3-60.2 +/- 0.4 is observed for treated membrane at 2-10 bar. The selectivity using mixed gas test at various CO2/CH4 compositions shows consistent results with the ideal gas selectivity. (C) 2012 Elsevier B.V. All rights reserved.