Radiation directly or indirectly affects human health. So, it is significant to work out the concentration of environmental radioactivity. The natural terrestrial radiation concentration level consists of Ra-226, Th-232, and K-40 concentrations. In this study, natural terrestrial radioactivity concentrations were examined in Sariyer district of Istanbul. Ra-226, Th-232, and K-40 concentrations were determined using a high-purity germanium detector (HPGe). The soil samples were collected from 18 different points within the boundaries of Sariyer district. The mean Ra-226 and Th-232 concentrations in this study were 30.78 +/- 2.26 Bq kg(-1) and 45.57 +/- 3.99 Bq kg(-1) respectively. K-40 concentrations were calculated as 863.70 +/- 48.70 Bq kg(-1). Also, radiological parameters were calculated and compared with limit value of world average.