Equilibrium, kinetics and thermodynamic studies on the removal of Acid Red 57 (AR57) by biosorption onto dried Cephalosporium aphidicola (C. aphidicola) cells have been investigated in a batch system with respect to pH, contact time and temperature. The results showed that the equilibrium time was attained within 40 min and the maximum biosorption capacity of AR57 dye onto C. aphidicola cells was 2.08 x 10(-4) mol g(-1) or 109.41 mg g(-1) obtained after contact with 0.4 g dm(-3) biosorbent concentration, pH(0) of 1 and at a temperature of 20 degrees C. The pseudo- second-order kinetic model was observed to provide the best correlation of the experimental data among the kinetic models studied. Biosorption isotherm models were developed and the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were conformed well to the experimental data. The changes of free energy, enthalpy and entropy of biosorption were also evaluated for the biosorption of AR57 dye onto C. aphidicola cells. (c) 2006 Elsevier B.V. All rights reserved.