A study on solvent extraction in multipass microporous hollow-fiber modules has been carried out both theoretically and experimentally. It was found that mass transfer of solvent extraction in multipass parallel-flow mass exchangers of microporous hollow-fiber modules can be analogous to heat transfer in shell-and-tube heat exchangers. Experiments were carried out with the use of Celgard X-10 microporous polypropylene hollow fibers as barriers to extract acetic acid from aqueous solution by methyl isobutyl ketone. Theoretical predictions are in agreement with the experimental results. In order to accomplish as much transfer of mass in as little space as possible, it is desirable to utilize multiple-fiber passes rather than using single-fiber pass.