The mathematical analysis of the multi-pass counter flow laminar mass exchanger with external recycle has been investigated theoretically. Using the orthogonal expansion technique associated with the eigenfunction expanding in terms of an extended power series to obtain the analytical solutions for the outlet concentration and mass transfer efficiency. The influences of three parameters, say the channel thickness ratio β, recycle ratio R, and physical property of permeable barrier γ, on the mass transfer efficiency were discussed. The analytical results of the multi-pass devices are represented graphically and compared with those of single- (without permeable barrier inserted) and double-pass operations (with one permeable barrier inserted) of the same working dimensions. There exists an optimal device performance of multi-pass mass exchangers with the suitable adjustment of the permeable barrier locations while both the mass transfer efficiency Im, and power consumption increment Ip, are considered.