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A new uranyl molybdate, Cs 2 [(UO 2 )O(MoO 4 )] (1), has been prepared by high-temperature solid-state reactions. The structure has been solved by direct methods and refined to R 1 ϭ 0.0284 for ΗF 0 Η Ն4σ F . The compound 1 is orthorhombic, Pca2 1 , a ϭ 12.018(2), b ϭ 12.438(2), c ϭ 17.917(3) Å , V ϭ 2678.2(7) Å 3 , Z ϭ 12. The structure of 1 is based upon one-dimensional chains consisting of corner-sharing UO 6 and MoO 4 polyhedra. The UO 6 square bipyramids share cis equatorial vertices to form zigzag chains that are further stabilized by bidendate MoO 4 tetrahedra. The chains have composition [(UO 2 )O(MoO 4 )] 2Ϫ and are oriented parallel to the c axis. In the structure, adjacent chains form pseudo-2D-layers parallel to (010). The Cs ϩ cations are in between the pseudolayers. The composition-structure relationships in alkali metal uranyl molybdates can be rationalized from the viewpoint of dimensional reduction using the following assumptions: (1) representation of * Prof. Dr. Sergey V. Krivovichev