The present study highlights the hydrogeological and hydrogeochemical characteristics of the CO2-rich thermal-mineral waters in Kayseri, Turkey. These waters of Dokuzpinar cold spring (DPS) (12-13 degrees C), Yesilhisar mineral spring (YMS) (13-16 degrees C), Acisu mineral spring (ACMS) (20-22.5 degrees C), Tekgoz thermal spring (TGS) (40-41 degrees C), and Bayramhaci thermal-mineral spring (BTMS) (45-46.5 degrees C) have different physical and chemical compositions. The waters are located within the Erciyes basin in the Central Anatolian Crystalline complex consisting of three main rock units. Metamorphic/crystalline rocks occur as the basement, sedimentary rocks of Upper Cretaceous-Quaternary age form the cover, and volcanosedimentary rocks Miocene-Quaternary in age represent the extrusive products of magmatism acting in that period. All these units are covered unconformably by terrace and alluvial deposits, and travertine occurrences have variable permeability. Dokuzpinar cold spring, YMS and ACMS localized mainly along the faults within the region have higher Na+ and Cl- contents whereas TGS and BTMS have higher amounts of Ca2+ and HCO3-. The high concentrations of Ca2+ and HCO3- are mainly related to the high CO2 contents resulting from interactions with carbonate rocks. Whereas the high Na+ content is derived from the alkaline rocks, such as syenite, tuff and basalts, the Cl- is generally connected to the dissolution of the evaporitic sequences. These waters are of meteoric-type. BTMS deviates from meteoric water line. The content is related to the increases in the 6180 compositions due to mineral-water interaction (re-equilibrium) process. CO2-dominated YMS and ACMS with low temperatures have higher mineralizations. Yesilhisar mineral spring, ACMS, TGS and BTMS are oversaturated in terms of calcite, aragonite, dolomite, goethite and hematite, and undersaturated with respect to gypsum, halite and anhydrite. Yesilhisar mineral spring, ACMS and BTMS are also characterized by recent travertine precipitation. Dokuzpinar cold spring is undersaturated in terms of the above minerals. The higher ratios of Ca/Mg and Cl/HCO3, and lower ratios of SO4/Cl in BTMS than TGS suggest that TGS has shallow circulation compared to BTMS, and/or has much more heat-loss enroute the surface. The sequence of hydrogeochemical and isotopic compositions of the waters is in an order of DPS > YMS > ACMS > TGS > BTMS and this suggests a transition period from a shallow circulation to a deep circulation path.