The incorporation of fillers, blending with multifunctional low molecular-weight additives and their combination are investigated as alternatives for modifying the permselective properties of polymeric gas separation membranes. For this purpose, pure polycarbonate (PC), PC/p-nitroaniline (pNA), PC/zeolite 4A and PC/pNA/zeolite 4A mixed matrix membranes were prepared by solvent-evaporation method using dichloromethane as solvent. Zeolite 4A was the filler and pNA was the low molecular-weight additive with multifunctional groups. The concentrations of pNA and zeolite 4A in the casting solution were changed between 1-5% (w/w) and 5-30% (w/w), respectively. Membranes were characterized by SEM, DSC and single gas permeability measurements of H-2, CO2, O-2, N-2 and CH4. Incorporation of zeolites to PC/pNA increased the T-g but the incorporation of them to pure PC had no effect on the T, suggesting that pNA induced an interaction between zeolite 4A and polymer matrix. The C/pNA/zeolite 4A membranes had lower permeabilities but higher ideal selectivities than pure PC and PC/zeolite 4A membranes. The membrane with 1% (w/w) pNA and 20% (w/w) zeolite 4A showed a selectivity of 121.3 for H-2 over CH4 and 51.8 for CO2 over CH4, whereas the H-2/CH4 and CO2/CH4 selectivities for pure PC membranes were 40.9 and 23.6, respectively. The gas separation performance of the PC membranes was remarkably improved with the incorporation of zeolite 4A and small amounts of pNA into the membrane formulation. (c) 2007 Elsevier B.V. All rights reserved.