BaTiO3-CaTiO3 and SrTiO3-BaTiO3 core-shell nanocubes were synthesized through the surface reconstruction of BaTiO3 nanocubes, which involved the reaction of titanium oxide with Ca(OH)2, Sr(OH)2, or Sr(OH)2·8H2O in water at 100 °C. The core-shell structure comprised a BaTiO3 nanocube core and a CaTiO3 or SrTiO3 shell. The outermost layer with a perovskite structure also comprised CaTiO3 or SrTiO3, and its thickness was several hundred picometers. The thinnest layer was constructed of only one layer of CaTiO3 or SrTiO3. This is the first presented work on a core-shell nanocube with the outermost layer consisting of only CaTiO3 or SrTiO3 surrounding the BaTiO3 nanocube. The shells of CaTiO3 and SrTiO3 comprise a layer thickness of only one unit cell of ∼0.4 nm (400 pm). Thus, we demonstrate new research on nanocube surfaces on the picometer scale.