The predicting equations for mass-transfer rate in the parallel-plate membrane extractor with a barrier of arbitrary location for double pass and recycle, have been derived by mass balance. Experimental works were carried out in a parallel-flow conduit of stainless steel inserted with a membrane sheet made of microporous polypropylene to extract acetic acid from aqueous solution by methyl iso-butyl ketone (MIBK). Theoretical predictions are qualitative agreement with the experimental results. The effects of barrier location and recycle ratio on the performance have been also discussed and compared. It was found for low flow rate that instead of setting large reflux ratio with the barrier location at the centerline, considerable improvement in mass transfer can be also achieved by setting low reflux ratio but with the barrier location moving away from the centerline to arrange the countercurrent-flow channel larger than cocurrent-flow channel. (C) 2003 Elsevier B.V. All rights reserved.