The aim of the present paper was to determine the content of phenolic compounds in fulvic acid extracts and the hydrolyzates of humic acids depending on their degree of maturity and plant litter properties. The research involved samples from organic and mineral horizons of forest soils. Phenolic compounds were identified with the chromatographic method (HPLC). The present research demonstrated that fractions of fulvic acids showed a higher content of aldehydes and phenolic acids as compared with the hydrolyzates of humic acid fractions. The parameter which differentiates humus acid properties of subhorizon Ol produced under different tree species is the ratio of the share of vanillyl, syringyl and cinnamyl compounds (V:S:C), while humification is connected with decreased content of aldehydes and phenolic acids which occur in hydrolyzates of humic acid fractions and fulvic acid extracts. In hydrolyzates of humic acid and fulvic acid fractions together with sampling depth, the values of parameter V+S+C decrease, which confirms that the parameter can be used to research the humification process of the plant material.