Orange platy crystals of K₂Na₈(UO₂) 8Mo₄O₂₄[(S,Mo)O₄], the first known uranium molybdosulfate, have been prepared by high-temperature solid-state reactions. The structure (monoclinic, C2/c, a = 24.282(4), b = 12.1170(18), c = 13.6174(17) Å, β = 106.33(1)°, V = 3845.0(9) Å3, Z = 4) has been solved by direct methods and refined to R₁ = 0.058 on the basis of 2837 unique observed reflections. The structure consists of a three-dimensional heteropolyhedral framework based upon the [(UO₂)4O ₄(Mo2O10)] layers parallel to (010). The layers are formed by linkage of chains of edge-sharing UO7 bipyramids running along the c axis via the Mo2O10 dimers of edge-sharing MoO6 octahedra. Linkage of the layers into a three-dimensional framework is provided by the MoO₄ and SO ₄ tetrahedra that share corners with the MoO6 octahedra. The Na ⁺ and K⁺ cations reside in framework cavities in between the uranyl molybdate layers. The structure of K₂Na ₈(UO₂)8Mo₄O₂₄[(S,Mo)O₄] is yet another complex derivative of the U₂MoO₈ structure type.