Abstract <p>The distribution and speciation of radium-226, uranium-238, and thorium-232 along the profile of soddy-podzolic-gley soil (Albic Stagnic Retisol) and in different size fractions of iron-manganic nodules, accounting for 17 wt % of the eluvial horizon, are described. Radionuclides are fractionated according to the Pavlotskaya method with additional separation of the organic matter fraction. The distribution of radionuclide specific activities along the soil profile follows the eluvial-illuvial pattern. The relative content of biologically available (water-soluble and exchangeable) and geochemically mobile (water-soluble, exchangeable, and true mobile) compounds decreases in the following order: radium-226 (11.9–28.5 and 15.3–32.5% of the total activities, respectively) &gt; uranium-238 (2.9–5.3 and 6.0–8.9%) &gt; thorium-232 (0.2–4.4 and 1.1–7.4%). As compared with the host soil mass of eluvial horizon, the nodules of all sizes accumulate radionuclides; the weighted average accumulation factors for radium-226, uranium-238, and thorium-232 amount to 2.1, 1.8, and 1.7, respectively. Regardless of the nodule size, radium-226 primarily accumulates in the exchangeable compounds; uranium-238, in the true mobile fraction; while thorium-232 accumulates depending on the size of nodules at the expense of the true mobile fraction and the compounds associated with organic matter and aluminum and iron oxides. The specific activities of radionuclides in the soil profile positively correlate with each other in a statistically significant manner, as well as with the content of typomorphic elements differentiated according to the eluvial–illuvial pattern, physical clay, and clay; they negatively correlate with the content of manganese and organic matter. In the eluvial horizon, thorium-232 positively correlates with iron and negatively, with calcium.</p>