The biosorption behavior of lanthanum and cerium ions from aqueous solution by leaf powder of Pinus brutia was separately studied in a batch system as a function of initial pH, contact time, initial metal ion concentration, temperature, and adsorbent amount. The uptake of lanthanum and cerium was increased when the initial pH of the solution was increased. Thermodynamic parameters such as standard enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were calculated and the results indicated that biosorption was endothermic and spontaneous in nature. The biosorption of lanthanum and cerium on powdered leaf of Pinus brutia was investigated by the Freundlich, Langmuir, and D-R isotherms. The results show that lanthanum and cerium adsorption can be explained by the Langmuir isotherm model and monolayer capacity was found as 22.94 mg g⁻¹ for lanthanum and 17.24 mg g⁻¹ for cerium. Desorption of lanthanum and cerium was studied using 0.5 M HNO₃ solution. The results suggested that powdered leaf of Pinus brutia may find promising applications for the recovery of lanthanum and cerium from aqueous effluents.