The extraction of uranyl from acidic (HNO3) aqueous solutions toward an ionic liquid phase, C1-C4-imTf2N (1-methyl,3-butylimidazolium Tf2N), has been investigated as a function of initial acid concentration and ligand concentration for two different extracting moieties: a classical malonamide, N,N′-dimethyl-N,N′-dibutylmalonamide (DMDBMA) and a functionalized IL composed of the Tf2N− anion and an imidazolium cation on which a malonamide pattern has been grafted (FIL-MA). The extraction mechanism, as demonstrated through the influence of added C1-C4-imCl or added LiTf2N in the aqueous phase, is slightly different between the DMDBMA and FIL-MA extracting agents. Modeling of the extraction data evidences a double extraction mechanism, with cation exchange of UO22+versus 2 H+ for DMDBMA or versus C1-C4 -im+ and H+ for FIL-MA at low acidic values, and through anion exchange of [UO2(NO3)3]−versus Tf2N− for both ligands at high HNO3 concentrations. The FIL-MA molecule is more efficient than its classical DMDBMA parent.