Abstract The coordination of U(VI) sulfate complexes has been investigated by uranium L _III-edge EXAFS and HEXS measurements with the aim to distinguish monodentate and bidentate coordinated sulfate in aqueous solution. UV-vis absorption spectroscopy has been used to differentiate the species and to determine the species distribution as a function of the [SO₄ ²⁻]/[UO₂ ²⁺] ratio. A monodentate coordination prevails in solutions with [SO₄ ²⁻]/[UO₂ ²⁺] ratio of 1, where UO₂SO₄ is the dominant species. Besides the dominating monodentate sulfate a small amount of bidentate sulfate could be observed, indicating that two isomers may exist for UO₂SO₄. With increasing [SO₄ ²⁻]/[UO₂ ²⁺] ratio the UO₂(SO₄)₂ ²⁻ species becomes the main species. The uranium atom of this species is coordinated by two bidentate sulfate groups.