At first diethylenetriaminepentaacetic acid (DTPA) was combined with a nanofiltration (NF) system in order to separate Gd3+ from La3+ ions in aqueous medium. Combined with a Sepa MG-17 NF membrane (Osmonics), it allowed Gd3+ retention to reach 95%, whereas La3+ retention only reached 50%. Then, to improve this one-step separation, new hydrophilic ligands were synthesized. Bis(diethanol)amide-DTPA 1 combined with a NF system involving a Sepa MG-17 membrane allowed Gd3+ retention to reach 87%, whereas La3+ retention remained at 5%. Finally, the same nanofiltration-complexation system was used to separate an equimolar aqueous mixture of Gd3+, Pr3+, and La3+ ions.