Water availability is a fundamental concern for coastal areas in arid and semiarid regions such as Jerba Island, southeastern Tunisia. In these areas, the water demand is steadily increasing and putting pressure on water resources. These pressures are maintained by excessive pumping to meet the needs of various agricultural, domestic, industrial and tourism sectors. The effects on the groundwater are expressed by a quantitative and qualitative deterioration of the regional ecosystem. An assessment of groundwater salinization and seawater intrusion in Jerba aquifer are therefore needed. Physical parameters were measured in situ in one hundred and three boreholes and major ions were analyzed and several diagram were used to model groundwater mineralization. Geochemical analysis revealed that Cl-Na-Mg-Ca-SO4 was the dominant water type indicating rock-water interaction and saltwater intrusion. Na+/Cl−, Ca2+/Cl−, Br−/Cl−, Ca2+/Na+, Mg2+/Ca2+ and Cl−/HCO3− ratios versus chloride confirms the double influence of mixing mechanisms of fresh and saline waters and the water-rock interactions. Computed seawater fraction for sampled water shows that the average mixing rate of seawater intrusion reached 10.5%, confirming the marine intrusion in the aquifer. The highest values were registered in coastal wells. The statistical analyses reveal that high groundwater mineralization is due to rock-water interaction associated with mixture of groundwater and seawater in many areas.