A detailed radiochemical investigation of interglacial peat from the stratotypical "Mikulino" section (Smolensk province) was carried out. The geochemical behavior of U and Th isotopes in the samples were studied and prerequistes for using uranium-thorium method for dating of terrestrial organogenous deposits, whose age is beyond the scope of the the radiocarbon dating method, were worked out. Determination of uranium and thorium contents was made in each 5-cm layer of peat with total thickness of 110 cm. It was found out that only 6 inner sections layers were closed geochemical systems with regard to U and Th and could be used for the uranium-thorium dating. This allowed us to estimate their direct absolute ages in the range from 89 ka to 108 ka. Applying of isochron method enabled additional contents of detrital U and Th to be taken into account as involved in the organic sample fractions during the radiochemical analysis. The age of the central section part corrected in this way yielded the dating of 113±11 ka. A detailed palynological analysis of each 10-cm peat layer of the section was carried out. Spore pollen diagram was built and showed 4 pollen zones (M5-M8) in accordance with the adopted subdivision scheme of the Last Inerglacial. The dated inner section layer corresponds to palynozones M6-M7. The results of a similarly comprehensive investigation of organognous deposits from the parastratotypical section "Nizhnyaya Boyarshchina" (Smolensk province) and the section "Fili Park" (Moscow City) are also given. The corrected ages of the inner section layers were 119,5±11,0 ka and 89±11 ka, respectively. The perspectives of ap plyng of ²³⁰Th/U dating method for organogenous terrestrial deposits as old 300-350 ka were discussed.