Abstract: A field investigation was carried out to determine the Physical and chemical characteristics of Al-Khobar aquifer in the Eastern region of Saudi Arabia. Total Dissolved Solids (TDS) varies from 4400 mg L-1 along the Gulf coast on the eastern side to around 1800 mg L-1 on the western side. Sodium (Na) is the dominant cation followed by Mg, Ca and K in descending order. Whereas, the anion concentration order is Cl > SO4 > HCO3. Nitrate concentration was found to be higher than the recommended limit for drinking purposes. The Saturation Indices (SI) indicated that the regional groundwater is under-saturated with respect to calcite, dolomite, gypsum, anhydrite, halite, pyrite and aragonite minerals and oversaturated with respect to goethite and hematite minerals. The hardness of groundwater is very high as compared to the established standards. The F contents are within permissible limits for drinking. The nitrate contents are within permissible limits for domestic use. Two water types i.e., Na-Ca-Cl-SO4 and Na-Ca-Mg-Cl-SO4 dominate the Al-Ahsa whereas Na-Ca-Cl and Na-Ca-Cl-SO4 water types are dominant in Al-Dammam, Al-Khobar and Al-Qatif areas. Overall, the study provided useful information on some important hydrogeochemical processes in groundwater of the eastern region. Further studies are required to determine heavy trace metals concentration for multiple uses.