In this study, we have prepared engineering polymer-based ionomers and pore-filled ion-exchange membranes (PFIEMs) employing a porous polyethylene substrate and combined them to fabricate the ionomer-PFIEM composite membranes for the reverse electrodialysis (RED) application. Both the electrochemical properties comparable to those of the commercial ion-exchange membranes (AMX/CMX, Astom Corp., Japan) and the physical stability adaptable to the practical uses have been achieved by integrating the ionomers having a high ion conductivity and the PFIEMs with an excellent mechanical strength. The RED performances have been evaluated by employing the prepared ionomer-PFIEM composite membranes and therefore excellent power generation performances were shown as the levels of 86.4% and 104.8% for the anion-exchange membrane and cation-exchange membrane, respectively, compared with those of the commercial membranes.