Barium dierbium(III) tetra-sulfide, BaEr2S4, crystallizes with four formula units in the ortho-rhom-bic space group Pnma in the CaFe2O4 structure type. The asymmetric unit contains two Er, one Ba, and four S atoms, each with .m. site symmetry. The structure consists of channels formed by corner- and edge-sharing ErS6 octa-hedra in which Ba atoms reside. The resultant coordination of Ba is that of a bicapped trigonal prism.