Barium titanate (BaTiO3) single-crystalline nanoparticles have been prepared via high temperature mixing method (HTMM) under hydrothermal conditions. The crystallized products were characterized by Xray diffraction (XRD), filed emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), Raman spectra, transmission electron microscopy (TEM). The BaTiO3 nanoparticles can be prepared at dilute KOH as compared with the method mixed at room temperature. The results show that the stoichiometric BaTiO3 nanoparticles were synthesized at [Ba/Ti](solution) = 1. The high temperature will significantly narrow the solubility difference between the barium and titanium sources and leads to a burst nucleation from the solution. The defect mechanism is used to illustrate the time-dependent transformation from cubic to tetragonal phase. Crown Copyright (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. All rights reserved.