Cubic perovskite-type barium stannate (BaSnO 3 ) powders were successfully prepared under hydrothermal conditions. Hydrothermal treatment of a highly reactive co-precipitated stannic hydroxide gel and barium hydroxide resulted to form a well-crystallized single phase of barium stannate powder via an intermediate phase of BaSn(OH) 6 . The optimum hydrothermal conditions of 573 K for 120 s were found for the formation of pure phase of BaSnO 3 . The synthesized product had a fine microstructure, with a grain size of ~7 μm. The formation of BaSnO 3 strongly depends on the reaction temperature.