The studied bogs of the Siedlce Heights in eastern Poland are currently undergoing decession. In the course of pedological studies, a significant modification of the structure of soil profiles caused by the murshing process was found. The TC/TN values (11.1–17.3) obtained in the study, as well as slight acidification (pHKCl 5.42–6.15) indicate the eutrophy of the studied soil environment, high biological activity and a significant degree of organic matter processing as a result of the processes of mineralization and humification. In addition, the upper levels covered by the process of murshing, compared to peat, are characterized by a lower carbon content and, most often, a similar nitrogen content. In the studied soils, humic substances are mostly represented by the fraction of humic acids. As a consequence, we note high values of the quotient expressing quantitative relations between soil humus fractions (HAs/FAs). For all profiles, the highest share of fulvic acids was recorded in turf murshic levels (M1). The occurrence of the most mature humic acids was found in peat levels not covered by secondary transformation processes after dehydration.