In this work, polycarbonate composite membranes were prepared for proton exchange membrane fuel cells (PEMFCs). In the preparation of membranes, a small amount of poly(ethylene glycol) (PEG) was blended with polycarbonate (PC) solution and then cast to make membranes. PEG contained in the membrane was removed by the high solubility of supercritical CO2 to afford porosity in the membrane. Then, porous PC membranes were soaked in Nafion® solution to yield the PC/Nafion® composite membranes. The PC composite membrane had lower ion conductivity but higher conductance than Nafion®.