Molecular dynamics simulation and Grand canonical Monte Carlo (GCMC) simulation are used to investigate the performance of Poly [1-trimethylsilyl-1-propyne] (PTMSP) membrane for organicvapor/permanent-gas separation. In general, the calculated diffusion and solubility coefficients of permanent gases and organic vapors in PTMSP are consistent with the experimental data, and correlate well with the square of the effective molecule diameter and critical temperature of each penetrant molecule. The simulation results reveal that the high organic-vapor/permanent-gas permeability selectivity of PTMSP can be attributed to the high organic-vapor/permanent-gas solubility selectivity. A comprehensive microscopic interpretation is provided based on the analysis of the center-of-mass displacements of penetrant molecules and the study of the free-volume size and distribution in PTMSP. (C) 2011 Elsevier B.V. All rights reserved.