Stability constants of some lanthanides with K22DAP (diaza-18-crown-6-diisopropionic acid) were determined by potentiometric titration method. The logarithmic values of these constants for La(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III), and Lu(III) are 11.14, 11.43, 11.78, 11.74, 11.95, 12.09, 11.49, and 10.88, respectively. Solvent extraction studies were carried out on the K22DAP complexes of La(III), Nd(III) and Lu(III) using TTA (thenoyltrifluoroacetone) as an extractant in different diluents. It appears that nitrobenzene, a diluent with high dielectric constant, favors the extraction of the complexes. Extraction rates of the K22DAP complexes of lanthanides were investigated at pH 5.5 and 8.0 with TTA in chloroform. The rates of extraction are found to be dependent upon the nature of the extracted species. Competitive extractions were carried out to see if selective extractions could be achieved.