Commercial proton ion exchange membranes (Nafion 117, Dufont, USA) are generally supplied in the form of Na⁺ to storage. Pretreatment accelerate the ionic conductivity of membrane by converting the surface of the membrane into the functional group (-SO₃H) having the form of proton ion. The pretreatment process may cause a significant increase in the total cost of water electrolysis and sometimes the expected results, i.e. reduction of membrane fouling, may not be achieved. In this study, we investigated the electrochemical characteristics of MEA according to the treatment condition of membrane and the type of catalyst such as Iridium black and Iridium oxide. Electrochemical and surface morphology of MEA were studied by I-V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM).