Various research issues related to soil organic matter in permafrost soils are still poorly investigated. At the same time, numerous investigations have shown the importance of permafrost soils, as they serve as a huge reservoir of organic matter. This work is aimed at the investigation of permafrost-affected soils in the southern part of the Yamal region, namely at the assessment of composition (fractional, elemental and molecular) of soil organic matter in topsoils formed under different biogeoclimatogenic conditions in tundra and forest tundra. Special attention was given to assessment of potential vulnerability of soil organic matter in the context of Arctic warming. Results showed the predominance of fulvic acids in the humus of the studied soils, which indicates mineralization risks in the humic substances system of Arctic soils under conditions of further warming. The13C-NMR analysis of humic acids revealed that all the studied soils are characterized by higher portions of aliphatic groups of carbon and decreased portions of aromatic groups and revealed early stages of the humification process in studied soils. These results contribute to scarcely distributed research of soil organic matter in permafrost soils of the Arctic. Moreover, our research provided new data on the vulnerability of soil organic matter and its possible mineralization risks under pronounced climate change in the Arctic using the modern instrumental technique.