One of the alternative methods for the treatment of animal by-products is their utilization in biological processes with a simultaneous production of energy-rich biogas. The results of the investigations of methane fermentation of animal waste are discussed in the study. The methane fermentation was carried out at 35°C. The substrates used in the experiments included poultry heads and muscle tissue. Furthermore, the fermentation residues subjected previously to hydrothermal processing were used as a substrate. The suspension of those substrates in the initial concentration range from 1 g TOC/dm3 to 11 g TOC/dm3 was used in the process. Additionally, the effect of the preliminary stage of hydrothermal substrate processing on methane fermentation efficiency was assessed. Poultry waste was subjected to thermohydrolysis at the temperature from 100°C to 300°C and pressure up to 9.0 MPa. The efficiency of the methane fermentation was estimated on the basis of biogas generated in the process. The biogas production was between 0.17 Ndm3/g TOC and 1.53 Ndm3/g TOC. In the case of poultry heads, a beneficial impact of hydrothermal processing at the temperatures from 100°C to 175°C was confirmed. For poultry meat the preliminary thermohydrolysis brought about a decrease of methane fraction in the biogas evolved. The preliminary hydrothermal processing made it possible to meet the requirements of legal regulations for the hygienization of by-products of animal origin. The obtained results allowed us to identify conditions under which the methane fermentation was carried out and which ensured a high level of methanization.