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Natural radioactivity is a source of continuous exposure to human beings. It originates from both extraterrestrial sources and radioactive elements in the earth's crust. The amount of radioactivity in soil varies widely. In Riyadh city, the capital of the Kingdom of Saudi Arabia, data on the levels of natural radioactivity in soils is absent. It was therefore considered imperative to measure the activity concentration of 226Ra, 232Th, and 40K in soil samples collected from various areas of Riyadh city. Activity concentrations were measured by means of high-resolution gamma-ray spectrometry. A total of 100 surface soil samples were collected from all over the Riyadh city. The measured activity concentrations of these radionuclides were compared with the data reported worldwide. Mean measured activity concentrations of 226Ra, 232Th, and 40K were 14.5\pm 3.9 Bq kg-1, 11.2 \pm 3.9 Bq kg-1, and 225 \pm 63 Bq kg-1, respectively. Mean values of radium equivalent activity, air absorbed gamma radiation dose rate, and external radiation hazard index were 47.8 Bq kg-1, 23.3 nGy h-1, and 0.13 Bq kg-1, respectively. The annual effective radiation dose was calculated to be 0.14 mSv y-1.