Two kinds of fixed carrier membrane materials containing secondary amine and carboxyl groups which can be used as carriers of CO2 were prepared. One was poly (N-vinyl-gamma-sodium aminobutyrate)(PVSA), which was obtained through the hydrolysis of polyvinylpyrrolidone (PVP) synthesized with N-vinylpyrrolidone(NVP) by radical polymerization. The other was poly(N-vinyl-gamma-sodium aminobutyrate-co-sodium acrylate)(VSA-SA), which was obtained through the hydrolysis of copolymer of N-vinylpyrrolidone and acrylamide(AAm) (NVP-AAm). The composite membranes were developed with PVSA or VSA-SA as active layer and polysulfone (PS) as support membranes. The permeation rates of pure CO2 and CH4 gas as well as binary mixtures of CO2/CH4 through the composite membranes were measured. The results show that the composite membranes present better CO2 permeation rates than other fixed carrier membranes do reported in literature. For example, at 26degreesC, 1330 Pa of CO2 pressure, the PVSA/PS composite membrane displays a CO2 permeation rate of 5.95 x 10(-7) cm(3) . cm(-2) . s(-1) . Pa-1 with CO2/CH4 ideal separation factor of 212.1. At 20 degreesC, 6400 Pa of CO2 pressure, the VSA-SA/PS composite membrane displays a CO2 permeation rate of 4.24 x 10(-8) cm(3) . cm(-2) . s(-1) . Pa-1 with CO2/CH4 ideal separation factor of 429.7. The results with the gas mixtures are not as good as those obtained with pure gas because of the coupling effects between CO2 and CH4. The heat cross-linked membrane shows good separation factor due to densification of the polymer.