Along with the Poland accession to the European Union, new legislations concerning waste management were introduced. The mushrooms subgrade is classified as an agricultural waste and because of this fact it has to be managed according with law rules. This waste is also potentially a good fertilizer. The experiments with composting of mushrooms subgrade mixed with other materials (sewage sludge, straw, liquid manure) were carried out in the Institute of Agricultural Engineering The aim of this research was to obtain compost which can be used as an agricultural fertilizer. During the experiments with the usage of bioreactor the presence of thermophilic phase was noticed. This phase is also indispensable for pasteurization of waste material and to decrease the risk of transfer of potential pathogens into the soil. The obtained compost has good physical characteristic. Usage as an admixture only the liquid manure had worse temperature effect than addition of liquid manure, straw and sewage sludge.