Abstract: The extraction of lanthanide picrate complexes with two derivatives of benzo-15-crown-5 into nitrobenzene and chloroform has been investigated. The determination of distribution ratios of seven lanthanides was carried out using their γ-radioactive isotopes as tracers and their γ-spectra were determined by high purity Ge-detector and a multichannel analyser.The extractability of the seven 4-tert-butylbenzo-15-crown -5 (t-BBC) complexes follows the following sequence: CeEu>Tm>Yb>Lu with a maximum at Sm. The polyether-cationic complexes were found to be of a 2:1 stoichiometry and the formation of a "sandwich" structure with a probable composition of Ln (t-BBC)2Pi3 seems indicated.The average value of separation factor is 1.14 for Ce and Sm, and 0.76 for Sm and Lu.The distribution ratio of lanthanides with t-BBC were twice as that with 4-bromo- benzo-15-crown-5. If chloroform is used as the diluent instead of nitrobenzene, the distribution ratio will decrease 20-fold.The addition of α-hydroxy-isobutyric acid into the aqueous phase can increase the separation factors for the heavy mass lanthanides.