The predicting equations for the mass-transfer rate and mass-transfer efficiency in a concentric circular membrane extractor module under concurrent-flow with various barrier locations were theoretically derived by calculating the mass balance on each subchannel. The separation variable with an orthogonal expansion technique extended in power series was used to obtain the analytical solution. The mass-trans. fer efficiency enhancement in this study is represented graphically with the volumetric flow rate, flow pattern and permeable-barrier location as parameters. Improvements in the extraction rate, extraction efficiency and mass transfer efficiency can be achieved by setting the barrier location moving away from a subchannel thickness ratio Of kappa = 0.5. The influences of the barrier location, extraction-phase flow rate, raffinate-phase flow rate and (he acetic acid concentration of the raffinate phase in the membrane extractor are also discussed.