The principal physico-chemical characteristics of some thermomineral waters of Rharb-Sais region (Morocco) are studied. The waters have a temperature between 24-40 °C and they are mainly chlorine-sodium type. The high concentrations of chlorides, sulphates, sodium, strontium, litium, barium and boron show a probably relationship with the dissolution of evaporitic salts. The minor undersaturated of some samples in gypsum, anhydrite and halite salts shows a water movement through more higly less soluble materials, mainly chloride and sulphate salts. Conventional chemical geothermometers show a base temperatures around 80- 100 °C.