The extraction of four lanthanide (La, Pr, Nd and Eu) picrates from water into 1,2-dichloroethane using 5,11,17,23 -tetra-tert-butyl-25,26,27,28-tetrakis(diphenylphosphinoylmethoxy)calix[4]arene as extracting agent has been studied. The extraction process takes place via formation of a species having a 1:1:3 metal/ligand/picrate ratio. The investigation of the extraction as a function of temperature between 10-25 degreesC reveals that the distribution ratio of metal ions decreases with increasing temperature. Thermodynamic parameters such as the free energy (DeltaG degrees), enthalpy (DeltaH degrees) and entropy (DeltaS degrees) changes were evaluated from the distribution measurements. The extraction process in all cases is exothermic with positive entropy changes.