The solution studies of some binary (1:1) and ternary (1:1:1) complexes of Eu(III), Gd(III), and Tb(III) with benzoic acid/its derivatives and uracil/its halo derivatives in dioxane−water (30:70 v/v) medium (ionic strength I = 0.1 mol·dm-3 NaNO3) have been performed. The experimental pH titration data were analyzed with the help of the BEST computer program in order to evaluate the formation constants of various intermediate species formed. The stability constants of the binary (1:1) systems decrease in order of Tb(III) > Eu(III) > Gd(III). The formation constant of 1:1:1 mixed ligand complexes for Eu(III), Gd(III), and Tb(III) with benzoic acid/its derivatives as the primary ligand and uracil/its halo derivatives as the secondary ligand has also been studied. The available data suggested that the ternary complexes of Eu(III), Gd(III), and Tb(III) are more stable than the crossponding binary complexes.