Water soluble salts are extremely destructive for stones and several treatment procedures are available for their removal. The most frequent desalination methods are based on two effects (diffusion and salt migration) but do not have a high efficiency. In another method direct electric field was applied but the treated objects showed symptoms of anodic destruction. The method of membrane electro-dyalysis reported here excluded this problem. Experiments were carried out by means of DDS and DDS2 dyalysers on samples of Karstand Pinczow limestones and Nietulisko and Zerkowice sandstones pretreated with a solution of sodium chloride but for Pinczow limestone samples treated with an aquaeous solution of potassium permanganate in order to evidence the ions migration in the desalination chamber. Results show that in the first stage of desalination, ions are transported mainly by diffusion; progressively the action of electric field and electroosmosis became more significant.