Gediz River drains a large area of the central Aegean region of western Turkey. The geological structure contains mostly metamorphic and volcanic rocks of the Palaeozoic, Mesozoic and Neogene ages. Water samples were collected from the river at 1-km intervals. The temperature, pH, Eh, specific conductivity, total alkalinity of the water, and beta and gamma activity in the vicinity of river were measured. The concentrations of radium and uranium in the water of Gediz River were determined by the collector-chamber and fluorimetric methods, respectively. The radium and uranium concentrations ranged from 0.021 to 1.041 Bq/l and from 0.4 to 10.4 ppb, respectively. Furthermore the temperature, pH, Eh, conductance, alkalinity of the water and gamma activity also varied between 10 and 30°C, 5.55 and 8.28,-108 and 36 mV, 8 and 5940 μS/cm, 94 and 750 mg/l and 56 and 176 cps, respectively. The reason for different radium values is probably the different geological structures in these three zones. The aim of this study was to determine the level of natural radioactivity in the Gediz Basin along the river, and whether this radiation causes any danger to health.