CubicBaTiO3 particles of10nmwere crystallized predominantly within the hydroxylated polybutadiene matrix of a phase separated triblock copolymeric thin film of polystyrene-polybutadiene-polystyrene (Kraton D1102). The barium titanated Kraton thin film had remnants of the cylindrical morphology of a plain Kraton thin film with an interdomain spacing of 23 nm. The procedure of barium titanation consisted of three steps: (1) in situ hydroxylation of the polybutadiene matrix of an annealed Kraton thin film, (2) regioselective deposition of barium titanium methoxypropanoxide (BaTi(OCH2CH(CH2)OCH3)6) on the hydroxylated polybutadiene matrix, and (3) hydrothermal reduction of the organometallic complexes in anNH3/H2Oatmosphere at 80 °C for 24 h. Isolated water clusters in step 3, condensed from theNH3/H2O atmosphere of 1 M NH4OH(aq) at 80 °C in the alkoxide-Kraton films, were believed to have a typical diameter of no more than 23 nm at a pH of 14. They gave a high pH environment to weaken the chelating effectamongalkoxides and the organic matrix and provided a spatial confinement for the localized nucleation and growth of cubic BaTiO3 nanoparticles.