Experimental study has been carried out to investigate the mass transfer behavior when carbon dioxide (CO2) is absorbed through microporous membranes with different porosities. Deionized water and sodium hydroxide (NaOH) aqueous solutions are chosen as absorbents. The effects of membrane porosity, absorbent pH value, and liquid velocity on mass transfer are studied. The effect of membrane porosity on mass transfer depends on both the absorbent pH value and liquid velocity. In the case of low pH values (7-11) in absorbent, membrane porosity almost has no effect on mass transfer at relatively lower liquid velocity, namely, the mass transfer coefficients based on the whole membrane area remain almost the same at different membrane porosities; the effect of membrane porosity on mass transfer becomes obvious with the increasing liquid velocity. Contrarily, as the absorbent pH value increases to 12 or 13, the influence of porosity on mass transfer coefficient becomes significant at varied liquid velocity. The modified mass transfer correlations are obtained with consideration of the effect of porosity over a varying membrane porosity range.