The potential of active and inactive biomass of various microorganisms as adsorbents (biosorbents) to remove pollutants such as heavy metals, synthetic dyes, phenolic compounds, and pesticides is being intensively studied. Medicinal mushrooms are a source of valuable biologically active compounds, which are extracted from the fruiting bodies of the mushrooms using suitable solvents. After extraction, the inactive extracted fungal biomass remains in the form of a filter cake. The aim of this study was to investigate the biosorption potential of the extracted inactive biomass of the fungus Fomitopsis pinicola for the removal of the synthetic dye methylene blue from aqueous model solutions. The effect of biosorbent concentration (0.4 g / L to 5 g / L), biosorption time (1 min to 240 min), initial dye concentration (10 mg / L to 150 mg / L), and pH values (4-10) of model dye solutions on the removal of methylene blue was studied.The percentage of dye removal increased as the mass concentration of the biosorbent increased and the contact time between the biosorbent and adsorbate increased. Increasing the initial mass concentration of the dye resulted in a decrease in the percentage of dye removal, but also increased the adsorption capacity. The biosorption efficiency was highest at a pH of 10, while it was lowest at a pH of 4. Analysis of the experimentally obtained data using the Freundlich and Langmuir equilibrium adsorption models showed that both models described well the process of methylene blue biosorption on inactive F. pinicola biomass. The results suggest that the extracted inactive biomass of the medicinal fungus F. pinicola has great potential for the remediation of wastewater contaminated with synthetic dyes.