The results of a study of the content of natural radionuclides (NRN) (226Ra, 232Th, 40K) and technogenic 137Cs in soil samples formed on red-brown clays collected at the period of time from 1927 to 2017 are presented. Soil sections were laid on the territory of the «Kamennaya Step’» wild life sanctuary and the island oak grove “Shipov Les” under three types of land: arable land, fallow and forest (forest protection belt. For the first time, data on the specific activity of NRN (226Ra, 232Th and 40K) was obtained in the soils of the “Kamennaya Step’’” wild life sanctuary and the island oak forest “Shipov Les” before the first nuclear tests (before 1954). The highest specific activity of NRN, as well as technogenic 137Cs, is observed in soils under forest, and the lowest: for radium-226 and cesium-137 in arable soils, and thorium-232 and cadium-40 in fallow soils. 137Cs was found in modern soil samples (0–20 cm), as well as in the 1962 sample (at a depth of 0–5 cm). Its specific activity varies in the range of 26.9–124.4 Bq/kg, with the highest content in soils under forest.