The article reports on the synthesis of three new organic ligands (s-triazine derivatives with salicylaldehyde and o-vanillin) and their complexes with uranyl(VI) salts. The uranyl(VI) complexes were characterized by single-crystal X-ray diffraction, UV–vis, fluorescence and IR spectroscopy. Thermal stabilities of the complexes were investigated using thermogravimetric analysis. The uranyl(VI) complexes are insoluble in water and are soluble in DMF and DMSO. This study contributes to the understanding of the coordination behaviour of the uranyl(VI) ion in organic polydentate ligands.