The objective of this work was to investigate the biosorption potential of the inactive biomass of the medicinal mushroom Fomitopsis pinicola for the removal of the synthetic dye Congo red (CR) from water. Various factors affecting the biosorption process were investigated in a batch procedure, testing the following factors: concentration of biosorbent (0.5 - 10 g/L), contact time (1 - 240 min), initial dye concentration (10 - 200 mg/L), and pH (4 - 10). The percentage of dye removal increased with increasing biosorbent concentration and contact time between biosorbent and dye. Increasing the initial dye concentration from 10 to 200 mg/L resulted in a decrease in the percentage of dye removal (from 89.11% to 31.89%) and an increase in the amount of dye adsorbed per gram of biosorbent (from 5.51 mg/g to 43.79 mg/g). Removal of CR from synthetic wastewater with the addition of dye (dye concentration from 10 mg/L to 100 mg/L) was as effective as removal of CR from model solutions, although the percentage of dye removal also decreased (from 96.75 to 62.6%) with increasing dye concentration. A higher percentage of dye removal or biosorption efficiency was achieved at a pH < 7. Equilibrium adsorption models (Freundlich and Langmuir) were used to analyze the experimentally obtained data. The results showed that the Freundlich model somewhat better described the biosorption process of CR on the inactive biomass of F. pinicola. The pseudo-second order kinetic model showed better agreement with the experimental data than the pseudo-first order model. The results suggest that the extracted inactive biomass of the medicinal fungus F. pinicola has the potential to be used in the remediation of wastewater contaminated with the synthetic dye Congo red.