The extraction of Nd3+ and Eu3+ from aqueous media containing selected diamine ligands by HDEHP solution in benzene has been investigated. It is found that the presence of the diamine in the aqueous phase enhances the extraction of both Nd3+ and Eu3 in the organic phase. The possible explanation for this behaviour is presented and a mechanism based on extraction of an adduct of the type MH3(DEHP)6. B is found to be the most probable.