Near-stoichiometric BaTiO3 powders with ultrafine particle size and high crystallinity were prepared by low temperature hydrothermal reaction of Ba(OAc)(2) and Ti(OCH2CH2OCH3)(4). BaTiO3 particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60-90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor, Ti(OCH2CH2OCH3)(4), which gives electronic, steric, and weakly chelating effect to titanium ion. Increasing the Ba/Ti mole ratio in reactant could not overcome the notorious Ba-deficiency but, improved stoichiometry and produced finer and less agglomerated particles. Interestingly, adding a slight pressure to autogeneous hydrothermal condition (total 4-10 atm) has yielded near-stoichiometric, highly crystalline, and less agglomerated BaTiO3 particles. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at below 400 degrees C.