Abstract: The study area is located on the southern rim of the Gediz Graben and to the west of Salihli town. In thestudy reported here, the hydrochemical characteristics of these geothermal fields were determined bychemical and isotopic data.The Menderes Massif rocks, which are formed by highly fractured karstic marbles, granodiorite,gneiss and guartz-schist units, are aquifers of the geothermal systems in the study area. The Neogeneterrestrial sediments, which are made up of alluvial deposits, act as cap rocks for the geothermalsystems. Alluvium is the most important unit for cold ground water production. The thermal springs inthe Sart-Çamur Spa have an outlet temperature of 52 °C and a 5 l/s discharge. Thermal fluid with atemperature of 155 ºC and a 2 l/s discharge was recorded at the drilling well, a well 1189 m deep, in theCaferbey geothermal field. The circulation of thermal fluid in the subsurface is along the fault andfracture zones.Results of environmental isotope and chemical analyses show that the thermal waters in thestudy area are of meteoric origin and generally have water-rock interactions. According to AIHchemical classifications, these thermal waters reflect the water types Na-Ca-HCO3 and Na-HCO3 in theSart-Camur and Caferbey geothermal fields, respectively. Cold waters are mainly dominated by HCO3¯and SO4¯ ions, with Na+2, Ca+2 and Mg+2 cations. High boron and arsenic contents are among thecontaminants when it comes to irrigation and drinking water sources in area. Because of these,reinjection of the thermal waters in the geothermal aquifer after use them is important, not only torecharge the reservoir but also to prevent harmful effects on the environment. According to variousgeothermometers, reservoir temperatures are calculated as varying between 8 oC and 290 ºC. Thethermal waters in the study area are oversaturated with respect to carbonate minerals (calcite andaragonite). These are most likely to cause scaling problems during extraction and use.