Cation conductive membranes, especially highly proton conductive membranes, are of interest not only for chlor-alkali electrolysis but for polymer electrolyte fuel cells as well. The very challenge for electrochemical characterization in this case is the low specific resistance of the polymer required for such applications, which in turn makes membrane resistance measurement a non-trivial problem. We investigate the different possibilities to characterize such membranes. For that purpose, a series of membranes made from sulfonated poly (phenylene oxide) (SPPO, degree of sulfonation (DS) from 7% up to 40%) was prepared. Commercially available membranes Nafion 117 as a reference are investigated, too. This contribution summarizes our new results concerning impedance spectroscopy measurements, using different measuring cells.