In this study, systematic measurement of activity concentrations of 40 K, 226 Ra, and 232 Th and radon exhalation rate has been done in soil samples of Cauvery River environment. The activity was measured using HPGe gamma-ray spectrometer, and the mean values of 40 K, 226 Ra, and 232 Th in the soil samples were found to be 182 ± 4, 34 ± 2, and 19 ± 1 Bq kg −1 , respectively. The radon exhalation rate was measured by "Can technique" using SSNTD (LR-115) films. The mean values of radium concentration, surface exhalation, and mass exhalation rate were found to be 118.95, 293.61, and 108.53 mBq kg −1 h −1 , respectively. The radiological hazard indices due to natural radioactivity were calculated and compared with international recommended values, which are lower than the recommended level. The radon exhalation rate is lower than the recommended level.