The sorption study of La(Ⅲ) was carried out on poly[dibenzo-18-crown-6] and L-valine medium. The quantitative adsorption of La(Ⅲ) was found at 1×10-2 to 1×10-5 mol/L L-valine. The various eluting agents were found efficient eluents for La(Ⅲ). The capacity of crown polymer for La(Ⅲ) was found to be 0.43 ±0.01 mmol/g. The tolerance limit of various cations and anions for La(Ⅲ) was determined. La(Ⅲ) was quantitatively separated from other metal ions in binary as well as multicomponent mixtures. The study was extended to sequential separation of La(Ⅲ), U(VI) and Th(IV). The good separation yields were obtained and had good reproducibility (±2%). The method incorporated the determination of La(Ⅲ) in real sample. The method was simple, rapid and selective. The sorption study of La (III) was carried out on poly [dibenzo-18-crown-6] and L-valine medium. The quantitative adsorption of La (III) was found at 1 x 10-2 to 1 x 10-5 The capacity of crown polymer for La (III) was found to be 0.43 ± 0.01 mmol / g. The tolerance limit of various cations and anions La (III) was quantitatively separated from other metal ions in binary as well as multicomponent mixtures. The study was extended to sequential separation of La (III), U (VI) and Th (IV). The good separation yields were obtained and had good reproducibility (± 2%). The method incorporated the determination of La (Ⅲ) in real sample. The method was simple, rapid and selective.