We describe the synthesis, structural and microstructural characterization of a strontium antimonate, Sr 1.5 Sb 0.5 O 3−y (y∼0.25), with a cubic, double-perovskite structure and a large concentration of oxygen vacancies with no apparent long-range order. High resolution electron microscopy indicates, however, that short-range ordering phenomena may occur. Electrical conductivity is independent of oxygen partial pressure (pO 2 ) for pO 2 <10 −1.25 atm, typical of ionic transport (σ∼10 −4 Scm −1 at 600°C), whereas the conductivity is dominated by p-type charge carriers at higher pO 2 .