Abstract: The solvent extraction of several lanthanide radionuclides(¹⁴⁴Ce, ¹⁴⁷Nd, ^152+154Eu,¹⁷⁰Tm and ¹⁶⁹Yb) from aqueous picric acid solutions with 4-methyl-benzo-15-crown-5 in chloroform has been investigated. The extracted species are found to be 1:2:3 (metal/crown/picrate) complex from slope analysis. The extraction equilibrium constants (K_ex) have been determined at 25°C. The order of K_ex values for trivalent lanthanide is Nd³⁺>Eu³⁺> Ce³⁺ >Tm³⁺ >Yb³⁺. This indicates that the ionic size of Nd³⁺(r = 0.995Å) may better match the cavity size of 4-methylbenzo-15-crown-5 than the ionic sizes of other lanthanides.In order to compare lanthanides with actinides, the extractability of 4-methylbenzo-15-crown-5 for Th⁴⁺, UO₂²⁺ and Am³⁺ has been determined.