The goal of the study was to investigate the fraction-group composition of humus podburs in southern Yakutia in relation to bioclimatic peculiarities of humus formation in the region. The objects of the study were raw-humic and dry-peatypodburs widely represented in the southern part of the Aldan plateau in the basins of the Iengra and Timpton Rivers (56- 57° N, 124-126° E) with absolute altitudes of 600-900 m above sea level. Morphogenetic characteristics of soils were described according to the new classification system of Rus- sian soils. General physical and chemical properties and granulometric composition of soils were determined by stand- ard techniques in soil science. The content and composition of humus were analyzed by Tyrin’s method modified by Ponomareva-Plotnikova. Examined podburs were character- ized by short humus profile (<50 cm) with a surface accumu- lation of a large amount of weakly-humificated organic matter. Another important characteristic of humus formation is high acidity of the environment. The main sources of organic mat- ter in these soils are moss-lichen larch forests with inclusions of Siberian dwarf pine, litterfall of which contribute to soil acid- ity when decomposing. It was revealed that fraction-group composition of podburs primarily demonstrated zonal biocli- matic characteristics of humus formation and were also char- acterized by similarity of group composition (humate-fulvate in accumulative horizons and fulvate in mineral horizons) as well as by similar structure of fractional composition of humic (HA) and fulvic acids (FA) with the dominance of “free” fractions HA- 1, FA-1 and FA-1a. These mobile humic acids along with coarse-grained granulometric composition directly participate in the formation of genetic type of podburs (intrasoil eluvial-illuvial redistribution of the acid mobile humus and the compounds of iron and aluminum associated with it).