Perovskite-type BaSnO3 powders with a particle size of 30-60 nm have been prepared from tin oxide hydrate (SnO2 center dot xH(2)O) gel via the hydrothermal synthesis route. The reactivity of the synthesized SnO2 center dot xH(2)O was found to be dependent on the pH value of the mixture of tin chloride and the ammonia solution. The most reactive SnO2 center dot xH(2)O 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)(6) phase in the as-prepared powder was found to convert into an amorphous phase other than into the BaSnO3 phase. The BaSnO3 powder crystallizing from the amorphous phase at 260. C for 4 h has better sintering properties than the commercial one. (c) Koninklijke Brill NV, Leiden and Society of Powder Technology, Japan, 2008