Agricultural terrains which are spontaneously irrigated by geothermal waters are affected by harmful contents of those waters especially boron. In the present study, Seferihisar-Doganbey Fault zone where thermal waters are exist, were selected as study area. In date interval July 2005-December 2007, water samples were collected in a month period from determined stations. Radon measurements in water samples were performed by using collector method. Also analysis of pH, EC (electrical conductivity), Na(2)CO(3), Na(+), K(+), CA(++) + Mg(++), Cl(-), HCO(3)(-), SO(4)(=) and B (Boron) have performed for those water samples. It is observed that radon changes for Cumali Station in interval of 0.1Bq/L-16.67Bq/L, for Karakoc Station in interval of 0.29Bq/L-10.26Bq/L, for Doganbey1 Station in interval of 0.33Bq/L -56.36Bq/L, for Doganbey 2 Station in interval of 0.34Bq/L-7.7Bq/L. Unstable variations of radon values provide requirement of periodical radon measurements along the study.