The reflux indeed has much influence on the heat and mass transfer, which in turn plays a significant role on the design, calculation, and operation of the equipment. The effects of recycle on membrane extraction through a double-pass parallel-plate channel have been studied both theoretically and experimentally. Theoretical analysis of mass transfer in multipass membrane extractors was analogous to heat transfer in multipass heat exchangers. Experiments were carried out with the use of a membrane sheet made of microporous polypropylene coated with polytetrafluoroethylene as a permeable barrier to extract acetic acid from aqueous solution by methyl isobutyl ketone. Theoretical predictions are in qualitative agreement with the experimental results. Constrast to a single-pass parallel-plate membrane channel without recycle, considerable improvement in mass transfer is obtainable if membrane extraction is operated in a double-pass device of same size with recycle which provides the increase of fluid velocity and pre-extraction (or pre-mixing) effect. It is found that recycle can enhance mass transfer, especially for operations with higher inlet volume rate or shorter conduit length.