Groundwater is the most important source of water supply in the Yeniceoba Plain in Central Anatolia, Turkey. An understanding of the geochemical evolution of groundwater is important for the sustainable development of water resources in this region. A hydrogeochemical investigation was conducted in the Plio-Quaternary aquifer system using stable isotopes (δ18O and δD), tritium (3H), major and minor elements (Ca, Na, K, Mg, Cl, SO4, NO3, HCO3 and Br) in order to identify groundwater chemistry patterns and the processes affecting groundwater mineralization in this system. The chemical data reveal that the chemical composition of groundwater in this aquifer system is mainly controlled by rock/water interactions including dissolution of evaporitic minerals, weathering of silicates, precipitation/dissolution of carbonates, ion exchange, and evaporation. Based on the values of Cl/Br ratio (> 300 mg/l) in the Plio-Quaternary groundwater, dissolution of evaporitic minerals in aquifer contributes significantly to the high mineralization. The stable isotope analyses indicate that the groundwater in the system was influenced by evaporation of rainfall during infiltration. Low tritium values (generally <1 tritium units) of groundwater reflect a minor contribution of recent recharge and groundwater residence times of more than three or four decades.