Studies were made on the membrane absorption of CO2 and/or SO2 using hydrophobic microporous hollow-fibre (HF) membrane modules. The absorbent liquids used were aqueous solutions of NaOH, K2CO3, alkanolamines and Na2SO3, flowing on the lumen side of the HF in laminar flow. A semi-empirical correlation was derived for the gas-phase mass-transfer coefficient on the shell side, by including geometrical factors of the HFs and the shell tube in the general correlation for mass transfer. It was found that the CO2 absorption rate in various aqueous solutions of alkalis and alkanolamines is successfully described by a model based on gas diffusion through the membrane pores subsequent to gas absorption accompanied by chemical reaction. The simultaneous membrane absorption of SO2 and CO2 was also studied using aqueous Na2SO3 solution, the selective removal of SO2 to CO2 being successfully achieved when both the liquid flow rate and solute concentration are low. This suggests that this membrane absorption method provides an energy saving process for SO2 removal from flue gases.