The main sources of radiation exposure are the inhalation of radon, thoron and their decay products released from the rocks and soil, and terrestrial gamma radiation. In order to estimate the potential effects, the radon and thoron concentrations in the soil gas, the radon measurements in the groundwaters and outdoor gamma dose rates were measured at 18 different locations in Büyükorhan in the south of Bursa, which granitoid unit takes up a vast space in this area. The radon and thoron concentrations in the soil gas were found to vary from 0.54 ± 0.01 kBq m −3 to 36.25 ± 0.98 kBq m −3 (mean value 11.54 ± 2.79 kBq m −3 ) and from 14.86 ± 1.21 kBq m −3 to 1462.50 ± 26.47 kBq m −3 (mean value 174.53 ± 87.35 kBq m −3 ), respectively. The measured radon concentrations in the groundwater samples ranged from 6.89 ± 1.11 to 61.43 ± 0.55 Bq l -1 (mean value 24.85 ± 4.36 Bq l -1 ). The measured outdoor gamma dose rates varied from 68 nGy h -1 to 369 nGy h -1 (mean value 129.7 nGy h -1 ). It was observed that radon and thoron concentrations in the soil gas are controlled by the lithology of the region. Additionally, the effect of the radon and thoron concentration in soil gas on outdoor gamma dose rate is indicated in the present study.