Concentrations of uranium series nuclides (238U, 226Ra, 210Pb), thorium series nuclides (228Ra, 212Bi), and potassium in soil of a granitic belt were examined in relation to their surface area of soil, clay mineral composition, and the SiO2 and Fe contents. In soil which is less weathered and has a surface area of around 10 m2/g, the 238U, 226Ra, 210Pb, 228Ra, and 40K contents increase with an increase the SiO2 content related to the elemental compositions of their parents rocks. In homologous soils resulting from progressive weathering, the 238U, 226Ra, 210Pb, and 228Ra contents are found to increase with increasing surface area. For an homologous soil which is free from the clay consisting of three-layer units, the 40K content decrease with increasing surface area. However, in an homologous soil which contains a clay consisting of three-layer units, the 40K content is not surface area dependent.