The title compound, Cs(3)(Mo(2)O(7))Br, was synthesized by the reaction of CsNO(3), MoO(3) and 1-ethyl-3-methyl-imidazolium bromide. Its crystal structure is isotypic with K(3)(Mo(2)O(7))Br and contains (MoO(4))(2-) tetra-hedra which share an O atom to produce a [Mo(2)O(7)](2-) dimolybdate(VI) anion with a linear bridging angle and m2 symmetry. The anions are linked by Cs atoms (site symmetry m2), forming sheets parallel to (001). Br atoms (site symmetry m2) are also part of this layer. Another type of Cs atom (3m site symmetry) is located in the inter-layer space and connects the layers via Cs-O and Cs-Br inter-actions into a three-dimensional array.