[en] The contents of natural uranium and radium radionuclides in the conjugated samples of soil and grass vegetation as well as in the pore soil solutions of the plant root nutrition area of Belarus natural ecosystems have been determined. The migration parameters of these radionuclides in the soil -- plant system for the different types of soil and various grass species of natural ecosystems have been established. It has been shown that the Bryophyta and lichen are characterized by higher accumulation of the natural uranium and radium radionuclides in comparison with the other grass species growing on the similar type of soil. An increase in the hydromorphity and acidity of the soil medium, as well as the proportion of uranium and radium in the soil solution of the root nutrition area intensifies the radionuclide soil-plant migration. (authors)