The aim of the present work is to demonstrate that an efficient all solid electric double layer capacitor (EDLC) may be realised with electrolyte membrane and carbon based electrodes prepared by using a Nafion ionomer solution. Polymer membrane was prepared by a casting method. Electrodes were prepared with two overlapped layers formed of a carbon–Nafion layer and a carbon paper substrate. Three different electrolyte separators in capacitor configuration have been tested and compared: (1) a commercial Nafion 115 membrane (N115), (2) a membrane prepared by casting the Nafion 1100 solution (NRG50) and (3) a porous glass fibre matrix impregnated with a 1 M H2SO4 solution (FVH2SO4). The membrane and electrodes assemblies (MEA) had thickness of 0.6–0.8 mm and geometric area of 4 cm2. The EDLCs characteristics have been studied by conductivity, cyclic voltammetry and DC charge–discharge methods. Proton conductivities of 5.7×10−2 and 3.1×10−2 S cm−1 have been measured at room temperature for the N115 and the NRG50, respectively. Specific capacity of 13.2 F g−1 has been obtained by capacitor utilising the cast Nafion membrane. This value is 70% of specific capacity obtained from the capacitor using sulphuric acid and about 140% of that using Nafion 115.