This work is focused on research of the biological degradation of organic materials used in the fermentation process for the production of the electrical and thermal energy on bioga splants. Thea im of this work is to evaluate the suitability on the contrary unsuitability ofe the selected substrates used for the biogas production. In the the theoretical part was processed problems biodegradation of the organic substances and theuse of different substrates in the process of methanisation. To evaluate the potential of selected substrates in the fermentation process were chosen test method using activated sludge from the wastewater plant. Significant indicators in the analysis of biological degradability are O2, CO2, BOD5 and CODCr.