Amine-modified epoxy resins were prepared by a mixture of an aliphatic epoxy resins (neo-pentyldiglycidyl ether) and polyether diamines (polyoxypropylene) as cross-linking agent. Four types of resins with different molecular packing structures were prepared by altering their cross-linking densities and hence their glass transition temperature. Gas phase permeation measurements show that the CO2 and N-2 transport through the present epoxy membranes obeys to the solution-diffusion mechanism. It is observed that, decreasing the cross-linking density both the membrane permeability and the CO2/N-2 selectivity increase. These findings reveal that the gas transport process is mainly dependent on the cross linking density which strongly affects the gas diffusivity while weakly changing the gas solubility. The change in gas diffusivity is discussed in the frame of polymer free volume theory. (C) 2015 Elsevier Ltd. All rights reserved.