Ion exchange membranes were prepared by grafting acrylic acid (AA) and methacrylic acid to the substrates such as microporous polyethylene (PE) and polytetrafluoroethylene (PTFE), and homogeneous poly[1-(trimethylsilyl)-1-propyne] (PTMSP) by the use of the plasma graft polymerization technique. Experiments on the facilitated transport of CO2 through the grafted membrane were carried out by using various diamines, diethylenetriamine and triethylenetetramine as the carrier. Among all the membranes tested, the AA grafted membrane containing ethylenediamine as the carrier showed the highest selectivity of CO2 over N-2. For example, when the CO2 partial pressure in the feed phase was 0.047 atm, the selectivity reached more than 4000 with 1.0 X 10(-4) cm(3)/(cm(2) s cmHg) of CO2 permeation rate. The use of PTFE and PTMSP substrates were effective for increasing the permeation rate of CO2. The effects of CO2 partial pressure in the sweep gas and temperature on the permeation rates and selectivities were also investigated. The CO2 partial pressure in the sweep gas hardly influenced the membrane efficiencies up to 0.023 atm.