The crystal structure of Ba4Os6O18Cl is described. Ba4Os6O18Cl, M(r) = 2013.97, cubic, I23, a = 9.380(1) Angstrom, V = 825.3(3) Angstrom(3), Z = 2, D-x = 8.104 Mg/m(3), lambda(MoKalpha) = 0.71069 Angstrom, F(000) = 1538, room temperature, final R(w) = 0.019 for 203 observed Friedel pairs. The structure is related to that of KSbO3 and is similar to that of La4Os6O19. The La4O groups are replaced by Ba4Cl groups.