A novel open-framework cadmium selenite bromide, [Cd10(SeO3)8Br4]·HBr·H2O (1), has been obtained by a solid-state reaction at 450°C, and the structure has been determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in Pbcm of the orthorhombic system: a=10.882(3), b=16.275(5), c=18.728(6)Å, V=3317(2)Å3, R1/wR2=0.0411/0.0659. Compound 1 is characteristic of a novel 3-D open-framework structure, composing ∞ 2[CdSeO3] layers and the pillars of edge-shared CdO3Br2 square pyramids. The lattice water molecules and the HBr molecules locate in the voids of the framework. Optical absorption spectrum of 1 reveals the presence of an optical gap of 1.65eV. Solid-state photoluminescent study indicates that compound 1 exhibits strong violet emission. TG–DSC measurement shows that compound 1 is thermally stable up to 200°C. [ABSTRACT FROM AUTHOR]