Hydrothermal synthesis was conducted with starting material as Barium hydroxide and hydrous titania (TiO2·xH2O) to obtain barium titanate fine Powder. The conversion, crystal structure and properties of as-prepared powder were investigated according to reaction temperature, time and concentration. The effect of variables on conversion was in order of time < temperature < concentration and the maximum conversion reached to 99.5% in the case of hydrothermal synthesis at 180 ℃ for 2 h with 2.0 M reactant concentration. At low concentration such as 0.25 M, formation of unreacted BaCO3 and TiO2 was not inevitable at even high reaction temperature and these components converted into BaTi2O5 at high temperature and remained as impurity. As concentration of reactant increased, the size of as-synthesized BaTiO3 powder deceased and Ba/Ti molar ratio approached into 1, showing Ba/Ti ratio of 1±0.005 for reaction at 180 ℃ for 2 h with 2.0 M concentration.