The extraction of the trivalent radioactive lantha-nides ( Ln) Pm and Gd from nitrate aqueous medium by 8-hydroxyquinoline ( HOX) and/or trilaurylamine ( TLA) trioctylamine ( TOA) tributylamine ( TBA),tripropylamine (TPA) or triallylamine (TAA ),L, in chloroform was investigated. The chemical formulae of the extracted organic phase species for both lanthanides were found Ln.NO3.( OX) for the chelate and Ln.NO3( OX)2.L for the adduct.The respective extraction and formation constants were evaluated. The synergic extraction of Pm and Gd by HOX-amine was investigated as a function of temperature. The thermodynamic parameters, free energy change, enthalpy change and entropy change were evaluated. The stoichiometry of the extracted organic phase species was established and the different data obtained were discussed.