Biosorption of Acid Blue 40 (AB40) onto cone biomass of Thuja orientalis was studied with variation in the parameters of pH, contact time, biosorbent and dye concentration and temperature to estimate the equilibrium, thermodynamic and kinetic parameters. The AB40 biosorption was fast and the equilibrium was attained within 50 min. Equilibrium data fitted well to the Langmuir isotherm model in the studied concentration range of AB40 and at various temperatures. Maximum biosorption capacity (q(max)) for AB40 was 2.05 x 10(-4)mol g(-1) or 97.06 mg g(-1) at 20 degrees C. The changes of Gibbs free energy, enthalpy and entropy of biosorption were also evaluated for the biosorption of AB40 onto T. orientalis. The results indicate that the biosorption was spontaneous and exothermic. Kinetics of biosorption of AB40 was analyzed and rate constants were also derived and the results show that the pseudo-second-order kinetic model agrees very well with the experimental data.