Antimony-containing solid solutions isostructural with bismuth tungstate, Bi 2 WO 6 , have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi 2 WO 6 . The Bi 2 W 1− x Sb x O 6− y solid solutions have been shown to exist in the composition range 0⩽x⩽0.05. We have examined the effect of Sb 5+ doping on the polymorphism and properties of Bi 2 WO 6 . In contrast to undoped Bi 2 WO 6 , antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960°C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb 5+ for W 6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi 2 WO 6 .