Mass transfer in mass exchangers, such as membrane extractors and dialysers, can be analogous to heat transfer in heat exchangers with correction-factor analysis. In present study, the expressions of mass-transfer rate and correction-factor charts for mass transfer in parallel-flow double-pass rectangular membrane modules were modified by the modified correction-factor analysis, instead of the conventional correction-factor analysis. They are explicit, instead of implicit in the conventional correction-factor analysis. The results can be readily calculated without using trial-and-error method. Experimental results confirm the predicted values for membrane extraction of acetic acid from aqueous solution by methyl isobutyl ketone, as well as for dialysing from aqueous solution, in the double-pass devices. (c) 2012 Canadian Society for Chemical Engineering