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 226Ra, 232Th, and 40K concentrations. In this study, natural terrestrial radioactivity concentrations were examined in Sariyer district of Istanbul. 226Ra, 232Th, and 40K 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 226Ra and 232Th concentrations in this study were 30.78 ± 2.26 Bq kg−1 and 45.57 ± 3.99 Bq kg−1 respectively. 40K concentrations were calculated as 863.70 ± 48.70 Bq kg−1. Also, radiological parameters were calculated and compared with limit value of world average.