Based on the analysis of fractional composition and the quality parameters of humic acids, the quality of organic matter from municipal sewage sludge with varying degrees of processing (unstabilized sludge, chemically stabilized sludge, sludge biologically stabilized under aerobic conditions, and sludge stored in lagoons) was assessed. The total organic carbon (TOC) content in sewage sludge depended on the sludge processing degree. Lime stabilization and composting had a positive effect on TOC content, but the TOC content was lower in stored sewage sludge than in raw sludge. The quality of organic matter in sewage sludge, assessed based on fractional composition, differed significantly from that of soil organic matter. The sludge contained less extractable humic compounds and more humins; the C – KH:C – KF index value was 0.5–0.7 in raw sludge and approximately 1 in lime-stabilized or composted sludge. The degree of humification of their organic matter was low (5.88–15.48%). Regardless of their origin, humic acids from sludge exhibited a similar elemental composition, distinct from that of soils – they contained less C and O and more H and N, indicating a higher proportion of aliphatic structures and a lower degree of aromatic nucleus condensation. Composting municipal sewage sludge is the most effective method of preparing it for use in agriculture and reclamation, as it ensures the formation of stable forms of humus, which promotes carbon sequestration and the sustainable improvement of degraded soil quality.