Single crystals of a new polymorph of the title compound, barium(II) 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone trihydrate, Ba2+.C6Cl2O4(2-).3H2O, have been grown in sodium metasilicate gel. Each Ba2+ cation is coordinated by eight O atoms. The Ba2+ cations are bridged by an O atom of a ligand around the centre of symmetry at Wyckoff position 4a and by the O atom of a water molecule around the centre of symmetry at Wyckoff position 4b, forming a sheet parallel to the (100) plane. Loose contacts are found around one of the water molecules, as observed in the Cmca form.