A membrane having an amine moiety was prepared by plasma-grafting 2-(N, N-dimethyl)aminoethyl methacrylate (DAMA) onto a microporous polyethylene substrate. Permselectivity of the membrane for CO2 over N-2 was achieved in both dry and water swollen conditions. When the CO2 partial pressure in the feed gas was 0.047 atm, the selectivity of CO2 over N-2 reached 130 for the highly swollen water containing membrane. This value was found to agree with that obtained with a mobile carrier membrane (supported liquid membrane) using DAMA as the carrier. The effects of several experimental conditions such as degree of grafting, feed partial pressure and temperature on the membrane performance were studied. It was suggested that the membrane acted as a fixed carrier membrane for CO2 facilitated transport in under the dry condition and acted as a fixed reaction site membrane in the water swollen condition. The carrier transport mechanism is discussed for dry and aqueous membranes.