In this study, gas separation properties of Matrimid/MIL-53 mixed matrix membranes with different MOF weight percentages (0-20 wt.%) were investigated. TEM, XRD and DLS analysis were implemented to investigate MIL-53, structure and particles size distribution. SEM, FTIR, DSC and TGA analyses were conducted to characterize the fabricated membranes. The SEM images of these membranes showed good adhesion between polymer and particles, although for 20% MIL-53 loading, particles agglomeration was observed in some areas. Moreover, surface images of the membranes showed adequate dispersion of the particles in the polymer matrix, especially at lower MOP loadings. The permeability of pure CO2 and CH4 gases for all membranes were measured and the ideal CO2/CH4 selectivity was calculated. CH4 permeability of membranes increased slightly as the percentage of loading increased. At 20 wt.% MOP loading, void formation led to a significant increase in CH4 permeability (300% over pure Matrimid). CO2 permeability showed the same trend; there was a 94% increase in permeability compared to pure Matrimid for 15 wt.% MMMs. CO2/CH4 selectivity also increased as MOF loading increased. The highest selectivity was shown for 15 wt.% MOP loading. This membrane had 84% growth in selectivity over pure Matrimid. Although at 20 wt.% MIL-53 loading, membrane separation performance was destroyed. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.