Nanocomposites have been extensively applied, and molecular dynamics simulation techniques have been applied to study the diffusion of gases (H-2, O-2, N-2, CO2, CH4, n-C4H10) through pure and filled with silica particle poly(1-trimethylsilyl-1-propyne) [PTMSP]. The aim for this research is to explore and investigate the effect of silica particle on the diffusion of gases in polymer. The diffusion coefficients of gases were determined via NVT molecular dynamics simulation using the COMPASS force field up to 500 or 1000 ps simulation time. We have focused on the effect of the concentration and the size of the silica particles on diffusion coefficients of gases and the changes of free volume and translational dynamics and intermolecular energies. It has been found that the addition of silica particle to PTMSP increased the diffusion coefficients of gases by enhancing the free volume of polymer. (c) 2006 Elsevier Ltd. All rights reserved.