The activity concentrations of 234U and 238U in thermal groundwater, deep well water and river water samples from Central Poland were determined. Concentration of 234U and 238U in the examined waters varied from <0.013 (LLD) to 16.8 mBq/dm3 and from <0.013 (LLD) to 45.5 mBq/dm3 respectively. The highest uranium activity concentrations were measured in the thermal groundwater from Mszczonow and Cieplice, while the lowest were observed in thermal ground water from Uniejow and Poddebice. In thermal groundwater from Skierniewice, uranium activity concentrations were below lower limit of detection (0.013 mBq/dm3). The 234U/238U activity ratio varied from 0.37 (Cieplice) to 1.30 (Poddebice well water).