The biosorption of lanthanum and cerium by leaves powder of Platanus orientalis was separately determined at varying experimental conditions using a batch technique. The effects of initial pH, contact time, initial metal ion concentration and temperature were investigated. The Langmuir and Freundlich isotherms were applied to represent the adsorption process. Langmuir isotherm fits the experimental data quite well. The Langmuir monolayer capacity of the sorbent is 28.65mg g(-1) and 32.05mg g(-1) for La,and Cc(III), respectively. Thermodynamic parameters such as standard enthalpy (Delta H degrees), entropy (AS') and free energy (Delta G degrees) were calculated from the slope and intercept of the plots of InKd versus 1/T. The results indicated that sorption was endothermic and spontaneous in nature. The work reveals that powdered leaf of Platanus orientalis is a good choice as a biosorbent for the recovery of lanthanum and cerium from aqueous solution. (C) 2007 Elsevier B.V. All rights reserved.