Tradeoff limitation on selectivity and permeability restricts the use of membranes for CO2 separation in natural gas industry. Mixed matrix membranes (MMMs) with combined advantages of polymeric matrix and inorganic fillers have been long proposed to overcome this shortcoming, but thick dense symmetric layer structure with a high mass resistance offers improvement in selectivity only. In this study, asymmetric polysulfone MMMs incorporated with small pore zeolite were proposed. SAPO-34 zeolite with a framework of 038 nm pore size and high CO2 adsorption affinity was used as inorganic fillers. The asymmetric mixed matrix membrane structure was prepared using the phase inversion method. The effects of zeolite loading (5-30 wt.%) on the membrane characteristics were studied using SEM with EDX, FT-IR, and TGA; while the gas transport properties were investigated using pure gas permeation tests of N-2, CO2 and CH4. Well dispersion of SAPO-34 particles in the polymer matrix was observed for zeolite loading less than 10 wt.%. The maximum CO2 permeance (314.02 GPU) was achieved by incorporating 10 wt.% of SAPO-34 into asymmetric PSf membrane. Even without strong binding between PSf and SAPO-34, CO2/N-2 and CO2/CH4 selectivities up to 26.1 and 28.2 respectively were observed. (C) 2013 Elsevier B.V. All rights reserved.