Liquid-liquid extraction of uranium(VI) (UO22+) from aqueous acidic (HCl and HNO3) solutions into a co-existing organic phase containing Alamine 308 (triisooctyl amine), TBP (tri-n-butyl phosphate) or CYANEX 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) and diluent (toluene) was studied at isothermal conditions (298.2 K) at aqueous phase acidity varying in the range 0.5-6 mol/dm(3). All solvent systems exhibit a maximum distribution ratio restricted in the acidity range 3-4 mol/dm(3). An obvious difference in extraction behavior through amine system has been observed for two acids, HCl and HNO3, distinguishing the divergent interactions attributed to the different mechanism of complexation depending on the acidic medium. The high degree of separation of UO22+ from HNO3 solution is feasible through a complex formation with extractants ranging in the order CYANEX 302 > TBP > Alamine 308. The results were correlated using various versions of the mass action law, i.e., a chemodel approach and a modified version of the Langmuir equilibrium model comprising the formation of one or at least two U(VI)-extractant aggregated structures.