Dibarium micro-oxido-bis[pentachloridoruthenate(IV)] decahydrate, Ba(2)Ru(2)Cl(10)O.10H(2)O, has been prepared from ruthenium(III) chloride and barium chloride in hydrochloric acid. It crystallizes in the monoclinic system (space group C2/c). The structure consists of alternating layers of [Ru(2)Cl(10)O](4-) and [Ba(H(2)O)(7)](2+) complex ions along the a direction. The O atom bonded to ruthenium occupies the 4e site, with 1 symmetry, while the other atoms occupy general 8f sites. The overall structure is held together by O-H...O hydrogen bonds and O-H...Cl dipole-dipole interactions.