To better understand the process of groundwater salinization around Sad Al Majnoon and Zima sabkhas, hydrochemical and isotopic analysis were performed. The two studied areas belong to the large basin of Bahira, with a semi-arid climate. From a topographical point of view, they are considered as low areas compared with the reliefs of Jbilet in the south, Mouissat in the west and Gantour in the north. These low areas represent the convergence points of a poorly developed runoff system. The Lutetian and the Plioquaternary formations are the most important aquifers. Groundwater converges towards areas of sabkhas where piezometric levels become shallow. The hydrochemical study shows that groundwater is brackish and salty. It is characterized by a chloride facies. The isotopic study shows that groundwater samples plots on evaporation lines. Salinization of groundwater should then be related to the recharge by evaporated water. The effects of water-rock interaction could also be involved due to the long residence time of the groundwater in the aquifers.