Perovskite-type BaSnO3powders with a particle size of 30-60 nm have been prepared from tin oxide hydrate (SnO2∙xH2O) gel via the hydrothermal synthesis route. The reactivity of the synthesized SnO2∙xH2O was found to be dependent on the pH value of the mixture of tin chloride and the ammonia solution. The most reactive SnO2∙xH2O gel was obtained at a pH value near 2. The hydrothermal products derived from this reactive gel were characterized with thermograrimetric/differential thermal analysis, Fourier transform infrared spectrometry, X-ray diffraction and high-resolution scanning electron microscopy. The BaSn(OH)6phase in the as-prepared powder was found to convert into an amorphous phase other than into the BaSnO3phase. The BaSnO3powder crystallizing from the amorphous phase at 260°C for 4 h has better sintering properties than the commercial one.