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The molecular structure of humus substances from permafrost-affected peat mounds of the East European forest-tundra has been studied with the use of up to date physicochemical methods (C-13 NMR, EPR spectroscopy). The structural-functional parameters of humus substances from these soils are specified by the integral action of cryogenic processes in the active layer, natural selection of aromatic structures in the course of humification, and by the species composition and degree of peat decomposition; they reflect the climatic conditions of peat formation in the Holocene. Humic acids of peat bogs are represented by low-condensed molecular structures with the low portion of carbon atoms of aromatic components, which increases down the soil profile, and by with the high content of non-oxidized aliphatic fragments. Active changes in the portions of aromatic and non-oxidized aliphatic fragments take place at the lower boundary of the active layer in the soils of bare peat spots. Such changes may serve as the basis for further search of the bioindicators of recent climate changes.