The interaction of the dioxouranium(VI) ion with five low molecular weight polyamines (ethylenediamine, putrescine, cadaverine, spermidine, and spermine) and with poly(allyl)amine (15 kDa) was studied potentiometrically (ISE-H(+) glass electrode) at T = 298.15 K. Investigations were carried out in NaNO(3) ionic medium, at l = 0.1 mol.L(-1) (and 0.5 mol.L(-1) for poly(allyl)amine only), in the pH range 3.5 to 5.5, before the formation of uranyl insoluble species. The results gave evidence for the formation of two species, namely, UO(2)L(2+) and UO(2)L(OH)(+) for the diamine systems (ethylenediamine, putrescine, cadaverine), UO(2)L(2+) and UO(2)LH(3+) for spermidine, and UO(2)LH(3+) and UO(2)LH(2)(4+) for spermine. In the system UO(2)-poly(allyl)amine, four species, namely, UO(2)L(2+), UO(2)LH(3+), UO(2)LH(2)(4+), and UO(2)L(OH)(+), are formed. Speciation profiles of the different systems and the sequestration capability of amines at various pH values are discussed. Some empirical relationships regarding the formation constants of complex species are also reported.