The objective of this work was to investigate the biosorption potential of extracted inactive biomass of the fungus Ganoderma applanatum for the removal of the synthetic dye Congo red (CR) from model dye solutions and synthetic wastewater. Batch adsorption experiments were conducted to investigate the influence of various factors on the biosorption process: Biosorbent concentration (1-5 \(g/dm^{3}\)), contact time (1-300 min), initial dye concentration (10-100 \(mg/dm^{3}\)), and pH (4-10). As the biosorbent concentration increased, the percentage of CR removal increased, while the amount of adsorbed CR per unit mass of biosorbent decreased. The biosorption process was dependent on the CR concentration. Increasing the initial dye concentration from 10 to 100 \(mg/dm^{3}\) resulted in an increase in the amount of dye adsorbed per gram of biosorbent (from 1.78 mg/g to 17.10 mg/g). pH values below 7 favor biosorption of CR on the inactive biomass of G. applanatum, resulting in a greater amount of dye adsorbed per unit mass of biosorbent as well as a higher percentage of dye removal. The Langmuir equilibrium model better described the biosorption process of CR on the inactive biomass of G. applanatum than the Freundlich model, while the kinetics of biosorption under the applied experimental conditions is better described by the pseudo-second-order kinetic model than by the pseudo-first-order model. The results indicate that the inactive biomass of the fungus G. applanatum has good biosorption potential for application in the remediation of wastewater contaminated with the synthetic dye CR.