The atomic-scale structure of nanocrystalline Ba xSr 1-xTiO 3 (x = 1, 0.5, 0) powders has been studied using high-energy X-ray diffraction, Rietveld refinement, and the atomic pair distribution function technique. The studies show that the materials are well-ordered at nanometer length distances. The three-dimensional atomic ordering in Ba 0.5Sr 0.5TiO 3 and SrTiO 3 nanopowders may well be described by a cubic structure of the perovskite type, similar to that occurring in the corresponding bulk crystals. The three-dimensional atomic ordering in BaTiO 3 is more complex. It is cubic-like on average, but locally shows slight distortions of a tetragonal-type. The new structural information helps one to understand better the dielectric properties of these nanomaterials.