Recently developed ETFE-SA membrane (sulphonated poly(ethylene-alt-tetrafluoroethylene)) has proved to be chemically stable in the direct methanol fuel cell (DMFC). According to methanol permeability measurements, the MeOH permeability through the ETFE-SA membrane is less than 2% of the corresponding value of the Nafion (R) membranes. The characterization of the ETFE-SA membranes is done with sophisticated microscopy techniques. The electrochemical inhomogeneity of the membranes is investigated with the scanning electrochemical microscopy (SECM) by mapping proton distribution across the membrane surface. The atomic force microscopy (AFM) is used, when the surface morphology and morphology changes originating from swelling are investigated, while with the scanning electron microscopy (SEM), the composition and the structure of the membranes can be clarified in detail. The sulphur profile along the membrane cross-section gives information about the distribution of sulphonic acid groups and it is detected with the SEM combined with a energy dispersive X-ray spectrometer. Surface hydrophobicity is investigated by water contact angle (CA) measurement. Many remarkable structural differences between different samples are observed during the measurements, e.g. the surface roughness of the ETFE-SA membrane is much higher, when compared to the Natione membranes. Altogether, the surface properties of the ETFE-SA and the Nafion (R) membranes are found to differ significantly from each other and the properties of ETFE-SA vary also as a function of manufacturing parameters. (c) 2006 Elsevier B.V. All rights reserved.