Fixed-carrier composite hollow-fiber membranes were prepared with polyvinylamine (PVAm) as the selective layer and a polysulfone ultrafiltration membrane as the substrate. The effects of the PVAm concentration in the coating solution, the number of coatings, and the crosslinking of glutaraldehyde and sulfuric acid on the CO2 permeation rate and CO2/CH4 selectivity of the composite membranes were investigated. As the PVAm concentration and the number of coatings increased, the CO2/CH4 selectivity increased, but the CO2 permeation rate decreased. The membranes crosslinked by glutaraldehyde or sulfuric acid possessed higher CO2/CH4 selectivities but lower CO2 permeation rates. For the pure feed gas, a composite hollow-fiber membrane coated with a 2 wt % PVAm solution two times and then crosslinked with glutaraldehyde and an acid solution in sequence had a CO2 permeation rate of 3.99 X 10(-6) cm(3) cm(-2) s(-1) cmHg(-1) and an ideal CO2/CH4 selectivity of 206 at a feed gas pressure of 96 cmHg and 298 K. The effect of time on the performance of the membranes was also investigated. The performance stability of the membranes was good during 6 days of testing. (c) 2006 Wiley Periodicals, Inc.