Interpolymer cation exchange membranes have been prepared from the system polyethylene/poly(styrene-co-divinylbenzene) [PE/poly(Stco-DVB)] by their sulfortation with a solution of chlorosulfonic acid in 1,2-dichloroethane. The membranes have been characterized electrochemically in mediator-less microbial fuel cell (MFC). MFC has worked on Escherichia coli bacteria with ferrocyanide as an oxidizer. Real-time voltage and current measurement gave us reliable results. Consequently, it was found that the amount of DVB in the copolymer is the main factor that determines the electrical efficiency of the membrane. (C) 2004 Elsevier B.V. All rights reserved.