The aim of the study was to evaluate the keratinolytic activity of 37 Trichophyton ajelloi strains, both pigmenting and non–pigmenting, isolated from loamy soil and chernozem, and to identify strains with the highest efficiency of converting feather waste into easily assimilable forms of nitrogen and sulfur for plants. The study showed that among Trichophyton ajelloi strains isolated from loamy soil, pigmenting strains were more capable of bio- degrading native feather keratin, while among the strains isolated from chernozem, non–pigmenting strains showed better abilities. The keratinolytic activity, as measured by feather weight loss after 42 days of culture, was on average higher in Trichophyton ajelloi strains isolated from loamy soil compared to those from chernozem. Extracellular keratinase activity, as well as release of soluble proteins and peptides in cultures of Trichophyton ajelloi strains isolated from loamy soil and chernozem increased throughout the experiment. Protease activity was high during the first 7 days of the experiment and increased again from day 28 of culture. The increase in the pH of the culture fluids was associated with the release of ammonium ions. The maximum release of ammonium and sulfate ions occurred on day 21 of culture. Three pigment–producing strains (No. III, XII, and XIV/XV) were among the most active in releasing large amounts of ammonium and sulfate ions. The biodegradation of feather waste by Trichophyton ajelloi strains can be used for the production of fertilizers suitable for the cultivation of plants, particularly those with high sulfur requirements.