In this research, Polyether Block Amide (PEBA) containing different loadings of alpha-Al2O3 particles was deposited on top of the polysulfone (PSf) supports to form PEBA 1657-alpha-Al2O3/PSf Multilayer Composite Mixed Matrix Membranes (MCMMMs). Multilayer composite structure was employed to overcome the sedimentation of fillers in the polymer matrix. Moreover, alpha phase of Al2O3 particles was applied to improve the distribution of these particles at higher loadings. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Fourier Transforms Infrared spectroscopy (FTIR) tests were applied to study morphology, crystalline structure, and chemical structure of the membranes, respectively. Gas permeation properties of the membranes were also measured using three different pure gases (CO2, CH4, and N-2) at a pressure of 7 bar and temperature of 25 degrees C. CO2 permeance and ideal selectivity of CO2/CH4 and CO2/N-2 for the optimum MCMMM with 20 wt.% loading of alpha-Al2O3 particles were 25% (117.5 Barrer), 81.5% (32), and 86.5% (57) higher than those of Multilayer Composite Neat Membrane (MCNM), respectively. The molecular simulation results confirmed the results of the experimental studies and approved that the alpha-Al2O3 particles were the right candidates to improve the PEBA performance for CO2 separation. (c) 2023 Sharif University of Technology. All rights reserved.