The aim of this work was to investigate the possibility of removing the cationic dye malachite green (MG) from model dye solutions and synthetic wastewater by biosorption on inactive waste biomass of the fungus Ganoderma applanatum. Batch adsorption experiments were performed to investigate the influence of various factors on the biosorption process: Biosorbent concentration (0.5 - 5 g/L), contact time (1 - 120 min), initial dye concentration (10 - 100 mg/L), and pH (4 - 10). An increase in biosorbent concentration resulted in an increase in the percentage of MG removal and a decrease in the amount of MG adsorbed per gram of biosorbent. The equilibrium condition was reached within 120 minutes, and the biosorption process was very fast in the first 30 minutes, while it slowed down in the later stages until equilibrium was reached. The biosorption process was dependent on the concentration of MG. An increase in the initial dye concentration from 10 to 100 mg/L was accompanied by an increase in the amount of MG adsorbed per gram of biosorbent (from 7.79 mg/g to 74.64 mg/g) and a decrease in the percentage of dye removal. pH values above 7 favor biosorption of MG on the inactive biomass of G. applanatum, as indicated by a greater amount of dye adsorbed per unit mass of biosorbent and a higher percentage of dye removal. The Freudlich equilibrium model better describes the process of biosorption of MG on the inactive biomass of G. applanatum compared to the Freundlich model. 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. A slightly larger amount of dye per gram of biosorbent was adsorbed in the removal from synthetic wastewater with dye addition than in the model dye solution.