The inventory of gamma-emitting radionuclides was determined in soil samples collected at six depth levels, from 15 locations in Istanbul metropolis. The activity concentrations of (232)Th, (238)U, (40)K were measured by means of gamma spectrometry. The average activity concentrations of (232)Th, (238)U, (40)K in the 30-cm depth soil were found as 32.1, 27.4, 393.1 Bq kg (-aEuro parts per thousand 1), respectively. The mean value of the absorbed dose rate (D), annual effective dose equivalent (AEDE) from the outdoor terrestrial gamma radiation, Ra equivalent activity (Ra(eq)), and the external hazard index (H (ex)) were calculated as 48.7 nGy h (-aEuro parts per thousand 1), 59.7 mu Sv, 104.1 Bq kg (-aEuro parts per thousand 1), and 0.28, respectively. The effects of organic matter content, textural properties, and pH value of soil samples on the natural radionuclide levels were also investigated. The relations between natural radionuclide level and the physical and chemical properties of studied soil samples were mainly clarified with cluster analysis and Pearson correlation.