The crystal structure of a new compound, (H₃O)[(UO₂)(SeO₄)(SeO₂OH)] (monoclinic, P2₁/n, a = 8.6682(19), b = 10.6545(16), c = 9.846(2) Å, β = 97.881(17)°, V = 900.7(3) ų), was solved by direct methods and refined to R ₁ = 0.050. The structure contains two symmetrically different Se atoms. The Se1 site is coordinated by three O atoms as is characteristic of Se⁴⁺ cations. The Se2 site is coordinated by four O atoms and forms selenate anion SeO₄²⁻. The structure is based on selenite-selenate sheets [(UO₂)(SeO₄)(SeO₂OH)]⁻ linked by the interlayer H₃O⁻ ions. The sheets are parallel to (101). The structure is compared to that of schmiederite, Pb₂Cu₂(SeO₃)(SeO₄)(OH)₄.