Asymmetric hollow fibre membrane modules coupled with a concentrated alkaline solution were investigated both experimentally and theoretically for the removal of H2S from gas streams. Each of the modules used consisted of a bundle of hollow fibres having an ultrathin layer at the outer edge of the hollow fibre. The hollow fibres were prepared from polysulfone/N-methyl-2-pyrrolidone/1-propanol and polyethersulfone/N-methyl-2-pyrrolidone/ethanol polymer solutions. A gas mixture containing 16-24 ppm of H2S was fed into the fibre lumen and was in countercurrent contact with a 10% NaOH solution fed in the shell side of the modules. The effects of membrane area, gas-phase velocity, feed gas pressure and membrane properties in terms of membrane resistances on H2S removal were examined. Laminar parabolic velocity profile was adopted to characterize the flow of the gas mixture in the hollow fibre lumen. The numerically calculated results agreed reasonably well with the experimental data in most cases. Both the experimental and the simulation results indicate that unless the resistance of the membranes approaches to zero, the radial concentration gradient of H2S in the hollow fibre lumen is always negligible for the H2S-NaOH (solution) system employed in this study.