The investigation was concerned with the qualification of the dynamics of changes in the biological activity of biomass obtained in the course of waste composting process. The results indicate accessibility of substrates for microorganisms, that is susceptibility to biodegradation. The measurements of oxygen demand were executed with the help of the OxiTop ® Control measurement system. The mixture of organic substrates was made up with additions of biodegradable wastes. The additions to the material for composting included meat–bone meal, waste edible oil, biodegradable foil as well as newspaper paper. The results of the investigations indicate high biological activity of the composts, continuing till the 60th day of the process. The wastes introduced to the composted biomass significantly differentiated the biological activity. In the case of material with addition of newspaper paper the activity got smaller after 40 days of composting, as opposed to the case of material with an addition of foil as well as the meal, where on the 40th day of the process an intensification of the biological activity was observed.