Li+- and K+-exchanged NASICON membranes have been prepared by an electromigration process from the Na3Zr2Si2PO12 compound. The exchanged rates are 30 and 43% against the initial Na+ molar content for K+ and Li+ ions, respectively. K+-exchanged NASICON pellets present important cracks due to the high increase of the 'c' crystallographic parameter. A proton insertion has been observed in the case of the Li+ exchange. Nevertheless Li+-exchanged NASICON membranes are sensitive both to Na+ and Li+ and present interesting selectivity properties. (C) 2003 Elsevier Science B.V. All rights reserved.