The biosorption characteristics of Cr(III) ions from aqueous solutions using the fungus Pleurotus ostreatus were investigated in terms of kinetics, equilibrium and thermodynamics.Optimum pH for Cr(III) biosorption was 5.5.The biosorption process of Cr(III) followed well pseudo first-order kinetics.Among the two-, three-, and four-parameter isotherm models tested, the Langmuir model exhibited the best fit to experimental data.According to Langmuir isotherm model, the maximum Cr(III) biosorption capacity of P. ostreatus is 110.9 mg/g, which is very close to the experimentally determined value (108 mg/g).Thermodynamic parameters (activation energy, and changes in activation enthalpy, activation entropy, and free energy of activation) revealed that the biosorption of Cr(III) onto P. ostreatus is an endothermic and non-spontaneous process.Results suggest that P. ostreatus is one of the best biosorbents hitherto reported for Cr(III) removal from aqueous solutions and could therefore be used effectively to detoxify wastewaters polluted with Cr(III).