The biosorption of neutral red, from aqueous solutions by Penicilium sp. biomass was studied in a batch system with respect to pretreatment methods, contact time, pH, initial dye concentration and temperature. The NaHCO3- treated biomass exhibited maximum dye uptake at pH 5-6. A larger amount of dye was removed by the pretreated biomass in the first 10 min of contact time and the equilibrium was established in 60 min for 50 mg/L of initial dye concentration. The optimum biosorption temperature was determined as 40 °C. Biosorption played main role in dye removal from aqueous solution in this study. The results indicate that the pretreated Penicilium sp. biomass can be used as an effective biosorbent to remove neutral red from aqueous solution.