[en] The formation of complexes between sodium 1.2-naphthoquinone-2-monoxime-5-sulphonate (L) and dioxouranium (VI) was studied in moderate acidic aqueous perchlorate solution. Formation constants for the complex species were analyzed using potentiometric and spectrophotometric titration data. The main species observed was [(UO₂)₂(OH₂)₂L₂]^2-. It was also synthesized separately and studied by NMR, IR and TG techniques. Thermal decomposition of the complex was also simulated in mass spectrometer to analyze the gaseous products first detached the complex